Method and system for pre-ignition control

ABSTRACT

Methods and systems are provided for improving the detection and mitigation of high speed pre-ignition. In one example, high speed pre-ignition is detected based on concurrent or sequential changes in an integrated knock sensor output in a knock window as well as a pre-ignition window. The high speed pre-ignition is addressed using cylinder fuel deactivation and/or engine load limiting to reduce the risk for run-away pre-ignition.

FIELD

The present description relates generally to methods and systems forpre-ignition detection and mitigation.

BACKGROUND/SUMMARY

Under certain operating conditions, engines that have high compressionratios, or are boosted to increase specific output, may be prone to lowspeed pre-ignition combustion events. During pre-ignition, combustion ofan air-fuel mixture in the cylinder is initiated before spark. The earlycombustion due to pre-ignition can cause very high in-cylinderpressures, and can result in combustion pressure waves similar tocombustion knock, but with significantly larger intensity. Variousstrategies have been developed for the detection and mitigation of lowspeed pre-ignition (LSPI) in lower engine speed ranges, where theoccurrence of pre-ignition tends to be higher. For example, pre-ignitionmay be detected and differentiated from knock using a knock sensor, andthen mitigated using cylinder enrichment, load clipping, torquelimiting, etc.

However, the inventors herein have recognized that pre-ignition can alsooccur at higher engine speeds, such as above 4000 rpm. Detection ofpre-ignition in this range may be more difficult to due to presence ofmechanical engine noise. If the high speed pre-ignition (HSPI) goesundetected, it can turn into “runaway pre-ignition” and potentiallycause rapid engine degradation.

The inventors herein have identified approaches to at least partiallyaddress the above issue. In one example approach, high speedpre-ignition may be better detected and addressed by a methodcomprising: indicating pre-ignition based on each of an integrated knocksensor output in a knock window and an integrated knock sensor output ina pre-ignition window. In this way, engine degradation due to high speedpre-ignition can be identified and mitigated.

As one example, an engine system may include one or more knock sensorsarranged in, at, or along an engine block or coupled to enginecylinders. Output from the knock sensor generated in one or more of afirst and second crank angle timing window may be used to identifyabnormal combustion, such as those due to knock and/or pre-ignition. Assuch, the first crank angle timing window may be a pre-ignition windowand the second crank angle timing window may be a knock window, whereinthe pre-ignition window occurs earlier (in the engine cycle) relative tothe knock window.

Sensor output generated in the knock and pre-ignition windows may beprocessed (e.g., band pass filtered, rectified, and integrated) todetermine respective output intensities. For example, output from theknock sensor may be integrated in each of the knock and pre-ignitionwindows to determine respective intensity of knock and pre-ignition.Further, output from the knock sensor generated in each knock window andpre-ignition window may be integrated over a plurality of engine cycles.Additionally, peak values within each of the knock and pre-ignitionwindows may be estimated for the plurality of engine cycles. High speedpre-ignition may be determined based upon the integrated output in eachof the knock and pre-ignition windows over the plurality of enginecycles. For example, high speed pre-ignition may be indicated when anincrease in the integrated sensor output in the knock window is followedby an increase in the integrated sensor output in the pre-ignitionwindow. As another example, high speed pre-ignition may be confirmedbased upon a decrease in peak values of knock sensor output in the knockwindow along with a concurrent increase in peak values of knock sensoroutput in the pre-ignition window over the plurality of engine cycles.Furthermore, upon determining the presence of high speed pre-ignition ina given cylinder, mitigating actions that are specific to high speedpre-ignition may be performed. For example, fuel injection into theaffected cylinder may be temporarily suspended, and intake air flowadjustments may be used to reduce the engine load.

In this way, high speed pre-ignition may be detected and alleviated. Thetechnical effect of monitoring a transition of abnormal combustionevents from knock windows to pre-ignition windows over a plurality ofengine cycles is that the presence of high speed pre-ignition may bedetected more accurately, without the results being affected (e.g.,corrupted) by mechanical engine noise. Further, an existing knock sensormay be used to identify high speed pre-ignition, and better distinguishit from low speed pre-ignition. As such, by identifying high speedpre-ignition reliably, and remedying the high speed pre-ignitionpromptly, durability of the engine may be extended and engineperformance may be enhanced.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic engine.

FIG. 2 depicts a high level flow chart for distinguishing low speedpre-ignition (LSPI) and high speed pre-ignition (HSPI).

FIG. 3 presents example mitigating actions for each of LSPI and HSPI.

FIG. 4 portrays example knock and pre-ignition windows, with and withoutoverlap that may be used for identifying HSPI.

FIGS. 5A and 5B illustrate example knock sensor outputs in overlappingand non-overlapping knock and pre-ignition windows when HSPI is present.

FIG. 6 shows an example routine for determining HSPI when the knock andpre-ignition windows are non-overlapping.

FIG. 7 is an example routine for determining HSPI when the knock andpre-ignition windows are at least partially overlapping.

FIG. 8 presents a block diagram depicting adjusting of engineload-limiting based on the output of the knock sensor generated in knockwindows and pre-ignition windows.

FIG. 9 illustrates an example detection and mitigation of HSPI when theknock and pre-ignition windows are non-overlapping.

FIG. 10 portrays an example detection of HSPI when the knock andpre-ignition windows are overlapping at least partially.

DETAILED DESCRIPTION

The following description relates to systems and methods for identifyingand mitigating high speed pre-ignition (HSPI) in an engine system, suchas the example engine system of FIG. 1. An engine controller may beconfigured to perform a control routine, such as the routines of FIGS.2, 3, 6, and 7, to detect HSPI based on the output of a knock sensorgenerated in each of an earlier pre-ignition window and a later knockwindow over multiple engine cycles (FIGS. 5A and 5B). The earlierpre-ignition window may either overlap or not overlap with the laterknock window (FIG. 4). Examples of HSPI detection with non-overlappingand overlapping windows are depicted in FIGS. 9 and 10 respectively.Various mitigating actions may be performed in response to detectingHSPI in one or more cylinders of the engine system. For example, fuelingof an affected cylinder may be discontinued. In another example, engineloads may be limited by reducing intake air flow. The controller mayadjust engine load limits based on a plurality of factors includingknock sensor output (FIG. 8). In this way, engine degradation due toHSPI may be reduced.

FIG. 1 depicts an example embodiment of a combustion chamber or cylinderof internal combustion engine 10. Engine 10 may receive controlparameters from a control system including controller 12 and input froma vehicle operator 130 via an input device 132. In this example, inputdevice 132 includes an accelerator pedal and a pedal position sensor 134for generating a proportional pedal position signal PP. Cylinder 14(herein also “combustion chamber 14’) of engine 10 may includecombustion chamber walls 136 with piston 138 positioned therein. Piston138 may be coupled to crankshaft 140 so that reciprocating motion of thepiston is translated into rotational motion of the crankshaft.Crankshaft 140 may be coupled to at least one drive wheel of thepassenger vehicle via a transmission system (not shown). Further, astarter motor may be coupled to crankshaft 140 via a flywheel (notshown) to enable a starting operation of engine 10.

Cylinder 14 can receive intake air via a series of intake air passages142, 144, and 146. Intake air passage 146 can communicate with othercylinders of engine 10 in addition to cylinder 14. In some embodiments,one or more of the intake passages may include a boosting device such asa turbocharger or a supercharger. For example, FIG. 1 shows engine 10configured with a turbocharger including a compressor 174 arrangedbetween intake air passages 142 and 144, and an exhaust turbine 176arranged along exhaust passage 148. Compressor 174 may be at leastpartially powered by exhaust turbine 176 via a shaft 180 where theboosting device is configured as a turbocharger. A wastegate (not shown)may be coupled across exhaust turbine 176 in the turbocharger.Specifically, the wastegate may be included in a bypass passage coupledbetween an inlet and outlet of the exhaust turbine 176. By adjusting aposition of the wastegate, an amount of boost provided by the exhaustturbine may be controlled. The wastegate may be coupled to anelectromechanical actuator which may receive commands from controller12. However, in other examples, such as where engine 10 is provided witha supercharger, exhaust turbine 176 may be optionally omitted, wherecompressor 174 may be powered by mechanical input from a motor or theengine.

A throttle 20 (also termed, intake throttle 20) including a throttleplate 164 may be provided along an intake passage of the engine forvarying the flow rate and/or pressure of intake air provided to theengine cylinders. For example, throttle 20 may be disposed downstream ofcompressor 174 as shown in FIG. 1, or alternatively may be providedupstream of compressor 174.

Exhaust passage 148 can receive exhaust gases from other cylinders ofengine 10 in addition to cylinder 14. Exhaust gas sensor 128 is showncoupled to exhaust passage 148 upstream of emission control device 178.Sensor 128 may be selected from among various suitable sensors forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO (as depicted), a HEGO (heated EGO), aNOx, HC, or CO sensor, for example. Emission control device 178 may be athree way catalyst (TWC), NOx trap, various other emission controldevices, or combinations thereof.

Exhaust temperature may be estimated by one or more temperature sensors(not shown) located in exhaust passage 148. Alternatively, exhausttemperature may be inferred based on engine operating conditions such asspeed, load, air-fuel ratio (AFR), spark retard, etc. Further, exhausttemperature may be computed by one or more exhaust gas sensors 128. Itmay be appreciated that the exhaust gas temperature may alternatively beestimated by any combination of temperature estimation methods.

An exhaust gas recirculation (EGR) system (not shown) may be used toroute a desired portion of exhaust gas from exhaust passage 148 tointake air passage 142 upstream of compressor 174. An amount of EGR flowmay be controlled by an EGR valve. Alternatively, a portion ofcombustion gases may be retained in the combustion chambers, as internalEGR, by controlling the timing of exhaust and intake valves. In yetanother alternative, exhaust gases from upstream of the exhaust turbinemay be directed to downstream of the compressor.

Each cylinder of engine 10 may include one or more intake valves and oneor more exhaust valves. For example, cylinder 14 is shown including atleast one intake poppet valve 150 and at least one exhaust poppet valve156 located at an upper region of cylinder 14. In some embodiments, eachcylinder of engine 10, including cylinder 14, may include at least twointake poppet valves and at least two exhaust poppet valves located atan upper region of the cylinder.

Intake valve 150 may be controlled by controller 12 by cam actuation viacam actuation system 151. Similarly, exhaust valve 156 may be controlledby controller 12 via cam actuation system 153. Cam actuation systems 151and 153 may each include one or more cams and may utilize one or more ofcam profile switching (CPS), variable cam timing (VCT), variable valvetiming (VVT) and/or variable valve lift (VVL) systems that may beoperated by controller 12 to vary valve operation. The position ofintake valve 150 and exhaust valve 156 may be determined by valveposition sensors 155 and 157, respectively. In alternative embodiments,the intake and/or exhaust valve may be controlled by electric valveactuation. For example, cylinder 14 may alternatively include an intakevalve controlled via electric valve actuation and an exhaust valvecontrolled via cam actuation including CPS and/or VCT systems. In stillother embodiments, the intake and exhaust valves may be controlled by acommon valve actuator or actuation system, or a variable valve timingactuator or actuation system.

Cylinder 14 can have a compression ratio, which is the ratio of volumeswhen piston 138 is at bottom center to top center. Conventionally, thecompression ratio is in the range of 9:1 to 10:1. However, in someexamples where different fuels are used, the compression ratio may beincreased. This may happen, for example, when higher octane fuels orfuels with higher latent enthalpy of vaporization are used. Thecompression ratio may also be increased if direct injection is used dueto its effect on engine knock.

In some embodiments, each cylinder of engine 10 may include a spark plug192 for initiating combustion. Ignition system 190 can provide anignition spark to combustion chamber 14 via spark plug 192 in responseto spark advance signal SA from controller 12, under select operatingmodes. However, in some embodiments, spark plug 192 may be omitted, suchas where engine 10 may initiate combustion by auto-ignition or byinjection of fuel as may be the case with some diesel engines.

In some embodiments, each cylinder of engine 10 may be configured withone or more fuel injectors for providing fuel thereto. As a non-limitingexample, cylinder 14 is shown including one fuel injector 166. Fuelinjector 166 is shown coupled directly to cylinder 14 for injecting fueldirectly therein in proportion to the pulse width of signal FPW receivedfrom controller 12 via electronic driver 168. In this manner, fuelinjector 166 provides what is known as direct injection (hereafter alsoreferred to as “DI”) of fuel into combustion cylinder 14. While FIG. 1shows fuel injector 166 as a side injector, it may also be locatedoverhead of the piston, such as near the position of spark plug 192.Such a position may improve mixing and combustion when operating theengine with an alcohol-based fuel due to the lower volatility of somealcohol-based fuels. Alternatively, the injector may be located overheadand near the intake valve to improve mixing. Fuel may be delivered tofuel injector 166 from a high pressure fuel system 8 including fueltanks, fuel pumps, and a fuel rail. Alternatively, fuel may be deliveredby a single stage fuel pump at lower pressure, in which case the timingof the direct fuel injection may be more limited during the compressionstroke than if a high pressure fuel system is used. Further, while notshown, the fuel tanks may have a pressure transducer providing a signalto controller 12. It will be appreciated that, in an alternateembodiment, fuel injector 166 may be a port injector providing fuel intothe intake port upstream of cylinder 14.

It will also be appreciated that while the depicted embodimentillustrates the engine being operated by injecting fuel via a singledirect injector; in alternate embodiments, the engine may be operated byusing two injectors (for example, a direct injector and a port injector)and varying a relative amount of injection from each injector.

Fuel tanks in fuel system 8 may hold fuel with different fuel qualities,such as different fuel compositions. These differences may includedifferent alcohol content, different octane, different heat ofvaporizations, different fuel blends, and/or combinations thereof etc.

Fuel may be delivered by the injector to the cylinder during a singlecycle of the cylinder. Further, the distribution and/or relative amountof fuel delivered from the injector may vary with operating conditions.Furthermore, for a single combustion event, multiple injections of thedelivered fuel may be performed per cycle. The multiple injections maybe performed during the compression stroke, intake stroke, or anyappropriate combination thereof. Also, fuel may be injected during thecycle to adjust the air-to-injected fuel ratio (AFR) of the combustion.For example, fuel may be injected to provide a stoichiometric AFR. AnAFR sensor may be included to provide an estimate of the in-cylinderAFR. In one example, the AFR sensor may be an exhaust gas sensor, suchas EGO sensor 128. By measuring an amount of residual oxygen (for leanmixtures) or unburned hydrocarbons (for rich mixtures) in the exhaustgas, the sensor may determine the AFR. As such, the AFR may be providedas a Lambda (λ) value, that is, as a ratio of actual AFR tostoichiometry for a given mixture. Thus, a Lambda of 1.0 indicates astoichiometric mixture, richer than stoichiometry mixtures may have alambda value less than 1.0, and leaner than stoichiometry mixtures mayhave a lambda value greater than 1. As described above, FIG. 1 showsonly one cylinder of a multi-cylinder engine. As such each cylinder maysimilarly include its own set of intake/exhaust valves, fuelinjector(s), spark plug, etc.

Engine 10 may further include a knock sensor 90 coupled to each cylinder14 for identifying abnormal cylinder combustion events, such as thoserelated to knock, low speed pre-ignition (LSPI) and high speedpre-ignition (HSPI). In alternate embodiments, one or more knock sensors90 may be coupled to selected locations of the engine block. The knocksensor may be an accelerometer on the cylinder block, or an ionizationsensor configured in the spark plug of each cylinder.

Controller 12 is shown as a microcomputer, including microprocessor unit106, input/output ports 108, an electronic storage medium for executableprograms and calibration values shown as read only memory chip 110 inthis particular example, random access memory 112, keep alive memory114, and a data bus. Controller 12 may receive various signals fromsensors coupled to engine 10, in addition to those signals previouslydiscussed, including measurement of inducted mass air flow (MAF) frommass air flow sensor 122; engine coolant temperature (ECT) fromtemperature sensor 116 coupled to cooling sleeve 118; a profile ignitionpickup signal (PIP) from Hall effect sensor 120 (or other type) coupledto crankshaft 140; throttle position (TP) from a throttle positionsensor; absolute manifold pressure signal (MAP) from sensor 124,cylinder AFR from EGO sensor 128, and abnormal combustion from knocksensor 90. Engine speed signal, RPM, may be generated by controller 12from signal PIP. Manifold pressure signal MAP from a manifold pressuresensor may be used to provide an indication of vacuum, or pressure, inthe intake manifold.

Storage medium read-only memory 110 can be programmed with computerreadable data representing instructions executable by processor 106 forperforming the methods described below as well as other variants thatare anticipated but not specifically listed. The controller 12 thusreceives signals from the various sensors of FIG. 1 and employs thevarious actuators of FIG. 1 to adjust engine operation based on thereceived signals and instructions stored on a memory of the controller.For example, adjusting an amount of intake air flow may includeadjusting an electromechanical actuator coupled to the intake throttle20 to modify an opening of intake throttle 20.

Controller 12 may receive output of the knock sensor and in combinationwith the output of a crankshaft acceleration sensor may indicateabnormal combustion events in the cylinder(s). Specifically, knocksensor output may be received for pre-defined windows (e.g., crank angletiming windows) and may be used to detect knock, low speed pre-ignition,high speed pre-ignition events, etc. Herein, signals from the knocksensor, such as a signal timing, amplitude, intensity, frequency, etc.,and signals from the crankshaft acceleration sensor for each of apre-ignition window and a knock window may be monitored. For example,the pre-ignition window may be an earlier crank angle timing window(e.g., before a cylinder spark event) while the knock window may be alater crank angle timing window (e.g., after the cylinder spark event)in the same cylinder cycle. As such, the pre-ignition window may occurearlier in an engine cycle while the knock window occurs later in thesame engine cycle for a common cylinder.

In one example, low speed pre-ignition (LSPI) may be indicated inresponse to knock sensor signals in the pre-ignition window that arelarger (e.g., higher than a first threshold), while knock may beindicated in response to knock sensor signals in the knock window thatare smaller (e.g., higher than a second threshold, the second thresholdlower than the first threshold). In another example, LSPI may beindicated based upon knock sensor signals in the pre-ignition windowthat are less frequent while knock may be indicated based upon sensorsignals in the knock window being more frequent. Thus, LSPI and knockindication may be based on comparison of knock sensor signals relativeto pre-defined thresholds within respective windows over an enginecycle.

The controller may also identify high speed pre-ignition and maydistinguish high speed pre-ignition (HSPI) from knock and/or LSPI. Forexample, HSPI may be identified based on the output of knock sensor 90in knock and pre-ignition windows over a plurality of engine cycles whenengine speed is higher than a threshold level. Herein, signals from theknock sensor for each of the pre-ignition window and the knock windowmay be received by the controller for a plurality of engine cycles. Thecontroller may then integrate the signals from the knock sensor for eachof the pre-ignition windows and the knock windows over the plurality ofengine cycles. HSPI may be indicated in response to an integrated knocksensor signal from a knock window that initially increases (e.g., tohigher than a third threshold, the third threshold higher than the firstand second threshold), followed by a rise in integrated knock sensorsignal in a pre-ignition window (e.g., to higher than a fourththreshold, the fourth threshold higher than the third threshold).Specifically, integrated sensor output in the knock windows during afirst, earlier number of engine cycles may increase to higher than thethird threshold. This increase may be followed by integrated sensoroutput in the pre-ignition windows rising to higher than the fourththreshold in a second, subsequent number of engine cycles.

As such, HSPI may be identified based on abnormal combustion eventsinitially occurring at later timings in the cylinder cycles (e.g., aftercylinder spark) and a subsequent transition of the abnormal combustionevents to earlier timings in ensuing cylinder cycles (e.g., earlier thancylinder spark). Thus, sensor output in the knock windows may be morefrequent and more intense (e.g., higher than the third threshold)relative to sensor output in the pre-ignition windows during a first,earlier number of engine cycles. However, in a second, later number ofengine cycles, sensor output in the knock windows may become lessregular and less intense while sensor output in the pre-ignition windowsconcurrently becomes more intense and more frequent. The controller maythereby also learn a gradual advancing of combustion initiation, andcorrelate that transition with the propensity for a high speedpre-ignition event. HSPI may also be detected based on peak values ofknock sensor output gradually moving from the knock windows to thepre-ignition windows. As such, HSPI may be indicated when peak values ofknock sensor signals in knock windows begin to decrease with aconcomitant rise in peak values of knock sensor signals in pre-ignitionwindows.

Thus, the controller may monitor and compare output from the knocksensor in a plurality of knock windows and pre-ignition windows overmultiple engine cycles to establish presence of HSPI. However, LSPI andknock may be detected by comparing knock sensor output to pre-determinedthresholds within a specific pre-ignition window and a specific knockwindow. Further, LSPI and knock may be identified without integratingknock sensor output over multiple engine cycles while HSPI may bedetected by integrating sensor output and comparing integrated sensoroutput over a plurality of engine cycles. It will also be appreciatedthat the inventors herein have recognized that each type of pre-ignition(LSPI and HSPI) may be mitigated in a distinct manner, which will bedetailed in reference to FIG. 3 below.

Turning now to FIG. 4, example knock and pre-ignition windows aredepicted for a cylinder in a single engine cycle in first map 410,second map 430, and third map 450. Specifically, first map 410 depictsnon-overlapping pre-ignition and knock windows while second map 430 andthird map 450 depict overlapping knock and pre-ignition windows. Thewindows are depicted in reference to a position of a piston within thecylinder shown along the horizontal axis. In particular, the exampleknock and pre-ignition windows are portrayed in reference to a top deadcenter (TDC) position of the piston when a spark event may occur. Thecontroller may detect pre-ignition and knock events based on output fromthe knock sensor in either overlapping or non-overlapping windows (e.g.,knock and pre-ignition windows).

It will be appreciated that the pre-ignition and knock windows discussedherein may be adjusted so as to capture a variety of abnormal combustionevents. Further, a size of the pre-ignition windows and the knockwindows may be varied based on engine parameters. In one example, thesize of each of the windows may be adjusted based on engine speed.Further, a size of the windows may be adjusted relative to one another.

First map 410 depicts a first example pre-ignition window 402 and afirst example knock window 404 with no overlap. Pre-ignition window 402occurs at an earlier crank timing relative to knock window 404 withinthe same engine cycle in the cylinder. Specifically, pre-ignition window402 begins before a spark event (e.g., before TDC) in the cylinder andends at TDC. Knock window 404, however, begins much after thepre-ignition window has ended (e.g., after TDC) and closes during asubsequent expansion stroke. As such, pre-ignition window 402 does notoverlap with knock window 404. To elaborate, pre-ignition window 402begins and ends before knock window 404 in the same engine cycle. In thecase of non-overlapping windows, knock sensor signals in thepre-ignition window may be assessed distinct from the knock sensorsignals in corresponding knock windows. Herein, HSPI may be determinedby tracking and comparing knock sensor signals in each of thepre-ignition and knock windows over numerous consecutive engine cycles.Likewise, LSPI may be determined by comparing knock sensor signals (notintegrated) in the pre-ignition window over an engine cycle relative toa pre-ignition threshold, while knock may be determined by comparingknock sensor signals (not integrated) in the knock window over an enginecycle relative to a knock threshold.

Referring now to FIG. 5A, it includes map 500 illustrating exampleschematic knock sensor outputs in two windows for two distinct enginecycles in a cylinder. The windows may either be knock windows orpre-ignition windows. Specifically, each of window 465 and window 475 inmap 500 of FIG. 5A may be knock windows or each of window 465 and window475 may be pre-ignition windows. Further, the windows may include knocksensor output for the same cylinder over two consecutive engine cycles:engine cycle ‘n’ and engine cycle ‘n+1’. Alternatively, the two enginecycles may not be consecutive and instead may be separated from eachother by at least one engine cycle. Specifically, engine cycle ‘n+1’ maybe subsequent to engine cycle ‘n’ and window 475 may follow window 465.

Window 465 of engine cycle ‘n’ includes knock sensor output in the formof curve 429. Further, curve 429 may include a plurality of peaks andvalleys as depicted. As an example, knock sensor output in window 465includes peaks 422, 424, 426, 428, as well as other peaks that are notnumbered. Window 475, which occurs in an engine cycle later than enginecycle ‘n’, shows an example knock sensor output in the form of curve439. Similar to curve 429, curve 439 may include a plurality of peaksand valleys as depicted. As an example, knock sensor output in window475 includes peaks 432, 434, 436, 438, as well as other peaks that arenot numbered.

The knock sensor output in a given window may be processed (e.g.,amplified, band pass filtered, rectified, integrated) to determine anoutput intensity for the given window. For example, output intensity forwindow 465 (IKO_1) may be determined by integrating the sensor outputwithin window 465 via an integrator (e.g., via summation over time as anapproximation to a time-based integral). Herein, output intensity inwindow 465 can be represented as area 425 (dotted area) under curve 429.Similarly, output intensity for window 475 (IKO_2) may be determined byintegrating the sensor output in window 475, and can be represented asarea 435 (area with vertical lines) under curve 439.

In one example, if window 465 (and window 475) is a knock window, theoutput intensity in window 465 may be compared to a first threshold todetermine the presence of knock. If window 465 is a pre-ignition window,output intensity in window 465 may be compared to a second threshold todetect the presence of LSPI. Herein, the second threshold may be higherthan the first threshold. In another example, a frequency of knocksensor output in the knock window may be compared to the first thresholdto indicate knock. Alternatively, a frequency of knock sensor output inthe pre-ignition window can be compared to the second threshold todetect presence of LSPI. In this case, the knock sensor output may notbe integrated. It will be noted that the frequency of knock sensoroutput as used in this disclosure implies an incidence or a number ofrecurring events or peaks.

The output intensities of each knock window and pre-ignition window mayalso be monitored over multiple engine cycles to establish the presenceof HSPI. It will be understood that output intensity of a window (e.g.,knock, pre-ignition) herein indicates an integrated knock sensor outputwithin the window (e.g., IKO_1 of window 465, IKO_2 of window 475). HSPImay be established by integrating output intensities of each knockwindow and each pre-ignition window over multiple engine cycles. Toelaborate, knock sensor output in knock windows may be integrated overmultiple engine cycles and knock sensor output in pre-ignition windowsmay also be integrated over a plurality of engine cycles. In the exampleof windows 465 and 475, HSPI may be determined by combining IKO_1 andIKO_2 to determine integrated output intensity.

As will be described in further detail in reference to FIG. 6, HSPI maybe indicated when integrated sensor output in knock windows overmultiple engine cycles increases to higher than a threshold outputfollowed by an increase in integrated sensor output in pre-ignitionwindows over multiple engine cycles. As such, output intensity in knockwindows may be initially higher (e.g., in earlier engine cycles) and maydecrease in later engine cycles while output intensities in pre-ignitionwindows may initially be lower (e.g., in earlier engine cycles) followedby an increase in later engine cycles.

In addition to determining output intensity in a window by integratingthe knock sensor output within the window, the controller may alsodetermine peak values within the window. The peak value may representthe peak intensity, or a peak amplitude. Peak values, as understoodherein, include a height of a peak (relative to a baseline of the knocksensor output) in the knock sensor output. For example, in window 465peak 424 has a peak value of PK_1 while peak 426 has a peak value ofPK_2. Further, peak 426 has a higher (e.g., highest) peak value thanother peaks in window 465. Similarly, the controller may determine peakvalues within window 475. For example, peak 434 in window 475 has a peakvalue of PK_3 while peak 438 has a peak value of PK_4. As shown, peak438 has a higher peak value than peak 434 in window 475. Further still,peak 438 has a higher (e.g., highest) peak value relative to other peaksin window 475. In one example, the peak value of the window may be theheight of the tallest peak in the knock sensor output. For example, peakvalue of window 465 may be PK_2 while peak value of window 475 may bePK_4. In another example, the peak value of the window may be an averageof all heights of all peaks in the knock sensor output. Peak values forwindows 465 and 475 may be estimated in alternate ways without departingfrom the scope of this disclosure. HSPI may also be indicated based onpeak values of knock sensor output in knock and pre-ignition windowsover the plurality of engine cycles. In particular, HSPI may be presentwhen peak values in knock windows decrease over the plurality of enginecycles with a simultaneous increase in peak values in pre-ignitionwindows.

Returning to FIG. 4, second map 430 of FIG. 4 portrays a second examplepre-ignition window 406 overlapping with a second example knock window408. Herein, pre-ignition window 406 starts from before a spark event(before TDC) in the cylinder and ends during an ensuing expansionstroke, while knock window 408 starts from after the spark event (afterTDC) in the cylinder and ends during the expansion stroke, after thepre-ignition window has ended. In other words, the pre-ignition windowends only after the knock window has commenced. Thus, knock window 408at least partially overlaps pre-ignition window 406.

In one example, when assessing for knock and LSPI in the overlappingwindows, a controller may first compare the output of the knock sensorin the pre-ignition window relative to a pre-ignition threshold. If theoutput is higher than the pre-ignition threshold and engine speed islower than a threshold (e.g., a speed threshold), LSPI may be determinedand each of engine fueling, air flow and spark timing may be adjusted.If the output in the pre-ignition window is not higher than thepre-ignition threshold, the output of the knock sensor in the knockwindow may be compared to a knock threshold. If the output is higherthan the knock threshold, knock may be determined and spark timing maybe adjusted.

To evaluate the presence of HSPI when receiving knock sensor output fromoverlapping windows, the controller may additionally or optionallydivide at least the pre-ignition window into a plurality of segments asshown in third map 450. Further, knock sensor output in each of theplurality of segments may be compared. Third map 450 includespre-ignition window 406 and knock window 408 of second map 430. Herein,pre-ignition window 406 is split into three segments: first segment 412,second segment 414, and third segment 416. It will be noted that thepre-ignition window may be split into a number of segments that isgreater than three or fewer than three without departing from the scopeof this disclosure. As such, the three segments of pre-ignition window406 are simply an example. The number of segments that the pre-ignitionwindow is split into may depend on an amount of overlap between theknock and pre-ignition windows. For example, the pre-ignition window maybe split into a higher number of segments if the degree of overlapbetween the knock and pre-ignition windows is greater. Alternatively, ifthe degree of overlap between the knock and pre-ignition windows islower, the pre-ignition window may be divided into fewer segments. Inanother example, the number of segments that the pre-ignition window isdivided into may also depend on engine operating conditions includingengine speed, load, spark timing, etc. In yet another example, thenumber of segments that the pre-ignition is split into may depend on theapplication (e.g., engine type).

In some examples, the knock window may be divided into a plurality ofsegments instead of splitting the pre-ignition window. In yet anotherexample, based on the degree of overlap between the windows, both theknock and pre-ignition windows may be segmented.

Referring now to FIG. 5B, example schematic knock sensor outputs in twosegmented pre-ignition windows are depicted in map 550. For example,each of pre-ignition windows 515 and 545 may overlap with correspondingknock windows (not shown) during engine cycle ‘p’ and engine cycle‘p+1’, respectively. To elaborate, pre-ignition window 515 may at leastpartially overlap a knock window in engine cycle ‘p’ while pre-ignitionwindow 545 may at least partially overlap a knock window in engine cycle‘p+1’. Accordingly, the pre-ignition windows may be segmented todetermine the presence of HSPI.

The segmented pre-ignition windows 515 and 545 may include knock sensoroutput for the same cylinder over two consecutive engine cycles: enginecycle ‘p’ and engine cycle ‘p+1’. Alternatively, the two engine cyclesdepicted in map 550 may not be consecutive and instead may be separatedfrom each other by at least one engine cycle. Regardless, engine cycle‘p+1’ may be subsequent to engine cycle ‘p’ and window 545 may followwindow 515.

Pre-ignition window 515 of engine cycle ‘p’ may be split into threesegments: first segment 501, second segment 503, and third segment 505.Further, pre-ignition window 515 includes knock sensor output in theform of curve 529 and each of the three segments include a portion ofcurve 529. Likewise, pre-ignition window 545 of engine cycle ‘p+1’ mayalso be split into the same three segments: first segment 501, secondsegment 503, and third segment 505. Further still, knock sensor outputin pre-ignition window 545 may be represented schematically as curve539. Each of the three segments of pre-ignition window 545 include aportion of curve 539. It will be noted that first segment 501 may occurearlier within an engine cycle relative to third segment 505 in theengine cycle. In other words, third segment 505 occurs at a later timethan the first segment 501 in the same engine cycle. As such, firstsegment 501 may be termed an earlier segment while third segment 505 maybe termed a later segment.

In order to determine HSPI using overlapping knock and pre-ignitionwindows, knock sensor output in the segments of the pre-ignition windowsmay be compared. In one example method, output intensity of each segmentmay be estimated by integrating knock sensor output within each segment.The output intensity for first segment 501 of pre-ignition window 515(IKO_Seg1) is represented by area 523 (slanted lines). Similarly,integrated knock sensor output for second segment 503 of pre-ignitionwindow 515 (IKO_Seg2) is represented by area 525 (horizontal lines) andintegrated knock sensor output for third segment 505 of pre-ignitionwindow 515 (IKO_Seg3) is represented by area 527 (crosshatched lines).In pre-ignition window 545, output intensity for first segment 501(IKO_Seg4) is represented by area 533 (slanted lines). Likewise, outputintensity for second segment 503 of pre-ignition window 545 (IKO_Seg5)is represented by area 535 (horizontal lines) and integrated knocksensor output for third segment 505 of pre-ignition window 545(IKO_Seg6) is represented by area 537 (crosshatched lines).

As depicted in map 550, within engine cycle ‘p’, which is earlier thanengine cycle ‘p+1’, output intensity in third segment 507 (IKO_Seg3) ofpre-ignition window 515 may be higher than output intensity in each ofsecond segment 503 (IKO_Seg2) and first segment 501 (IKO_Seg1). Further,integrated sensor output in the first segment 501 of pre-ignition window515 may be lower than second segment 503. To elaborate, area 527 inlater segment (e.g., third segment 505) of pre-ignition window 515 maybe higher than that in the earlier segments of pre-ignition window 515.In other words, output intensity in the later segment may be higher thanthat in the earlier segment during an early engine cycle.

Further still, in the subsequent engine cycle ‘p+1’, integrated sensoroutput in third segment 505 (IKO_Seg6) of pre-ignition window 545represented by area 537 may decrease relative to integrated sensoroutput in third segment 505 (IKO_Seg3) in pre-ignition window 515. Atthe same time, integrated sensor output in first segment 501 ofpre-ignition window 545 (IKO_Seg4) may be higher than each of integratedsensor output in the first segment 501 of pre-ignition window 515(IKO_Seg1) and integrated sensor output in third segment 505 (IKO_Seg6)of pre-ignition window 545 represented by area 537.

As mentioned earlier, HSPI may be identified in general when combustioncommences at (or transitions towards) earlier times in an engine cyclerelative to preceding engine cycles. In the example of segmentedpre-ignition windows 515 and 545, HSPI may be indicated in response tooutput intensity in later segments (e.g., third segment 505) beinghigher than output intensities in earlier segments during initial enginecycles (e.g., engine cycle ‘p’) followed by a decrease in outputintensity in later segments and an increase in output intensity inearlier segments during ensuing engine cycles (e.g., engine cycle“p+1’).

While pre-ignition windows 515 and 545 show a transition in combustionevents from the later, third segments to the earlier, first segmentsover two engine cycles for ease of explanation, the progression ofcombustion events from later segments to earlier segments in actualitymay occur over a larger number of engine cycles. For example, outputintensity may initially be higher in the later, third segments. This maybe followed by a gradual rise in output intensity in middle, secondsegments over a plurality of engine cycles, while concurrently theoutput intensity in the later, third segments starts to fall. Duringthis entire time, the output intensity in the earlier, first segmentsmay be lower than each of the middle and later segments. As the numberof engine cycles increases, output intensity in the earlier, firstsegments may increase steadily as output intensities in the each ofmiddle, second segments and later, third segments diminish steadily. Inthis way, the knock sensor output intensity may gradually transition(herein, advance) from later segments of a window to earlier segments ofa window over time (counted here in terms of engine cycles). Thisgradual advancement of combustion initiation may be correlated with thepresence of HSPI.

In another example, peak values of the segments in the pre-ignitionwindows may be compared to identify HSPI. As described earlier, peakvalue may be represented by a height of a peak in an example knocksensor signal. Curve 529 in pre-ignition window 515 may include aplurality of peaks and valleys as depicted. As an example, knock sensoroutput in pre-ignition window 515 in engine cycle ‘p’ includes peaks 522and 524 in first segment 501, peak 526 in second segment 503, and peaks528, 530, and 532 in third segment 505 (amongst other peaks that are notnumbered). Third segment 505 of pre-ignition window 515 includes peak532, which has a peak value of PK_8 while peak 530 has a peak value ofPK_7. Meanwhile, second segment 503 of pre-ignition window 515 in thesame engine cycle ‘p’ has peak 526 with peak value PK_6 while peak 524in first segment 501 of pre-ignition window 515 has peak value PK_5. Asdepicted, peak values in the earlier, first segment are lower than thosein each of the middle, second segment and later, third segments.Further, peak 532 in the third, later segment has a higher (e.g.,highest) peak value than other peaks in window 515. Thus, peak values inthe later, third segment 505 may be higher than those in each of middle,second segment 503, and earlier, first segment 501 during an earlierengine cycle such as engine cycle ‘p’.

Pre-ignition window 545, which occurs in an engine cycle later thanengine cycle ‘p’, shows an example knock sensor output in the form ofcurve 539. Similar to curve 529, curve 539 may include a plurality ofpeaks and valleys as depicted. As an example, knock sensor output inpre-ignition window 545 in engine cycle ‘p+1’ includes peaks 534 and 536in first segment 501, peak 538 in second segment 503, and peak 542 inthird segment 505, as well as other peaks that are not numbered. Asshown in pre-ignition window 545, peak value of peak 542 in thirdsegment 505 is PK_10, which is significantly lower than peak value PK_8of peak 532 in third segment 505 of pre-ignition window 515. In otherwords, peak values in the later segments have decreased over multipleengine cycles. At the same time, peak value in first segment 501 ofpre-ignition window 545 (e.g., of peak 536) is PK_9 which isconsiderably higher than each of peak value PK_10 and peak value PK_5 infirst segment 501 of pre-ignition window 515. Thus, peak values in theearlier, first segments undergo an increase over multiple engine cycles.As engine cycle ‘p+1’ is subsequent to engine cycle ‘p’, HSPI may beindicated based on the decrease in peak values in the later, thirdsegment and a simultaneous increase in peak values in the earlier, firstsegments over multiple engine cycles. In this way, peak values of theknock sensor output may gradually transition (herein, advance) fromlater segments of a window to earlier segments of a window over time(counted here in terms of engine cycles). This gradual advancement ofcombustion initiation may be correlated with the presence of HSPI.

In this manner, HSPI may be identified with overlapping pre-ignition andknock windows. While the above examples illustrate splitting only thepre-ignition window into segments, in other examples, the knock windowmay, additionally or alternatively, be split into segments. In anotherexample, only one of the knock and pre-ignition windows may be segmentedwhen window overlap occurs. The number of segments that the knock windowis divided into may be based upon a degree of overlap existing betweenthe knock and pre-ignition windows, the number of segments increased asthe degree of overlap increases. Similar to comparing segments in thepre-ignition windows over a plurality of engine cycles, knock sensoroutput within the segments of the knock window maybe compared overmultiple engine cycles. HSPI may be confirmed when output intensities inlater segments are initially higher than output intensities in earliersegments followed by a decrease in output intensities in later segmentsas a number of engine cycles increases. At the same time, outputintensity in earlier windows may also rise as the number of enginecycles increases. In other words, HSPI may be confirmed by observing amovement of combustion initiation from later segments to earliersegments over multiple engine cycles.

Turning now to FIG. 2, it depicts an example routine 200 illustratingdetection of various abnormal combustion events such as knock, LSPI, andHSPI. Specifically, engine speed and output from a knock sensor, such asknock sensor 90 of FIG. 1, in a knock window and a pre-ignition windowmay be utilized to differentiate between knock, LSPI, and HSPI. As such,routine 200 will be described in relation to the engine system shown inFIG. 1, but it should be understood that similar routines may be usedwith other systems without departing from the scope of this disclosure.Instructions for carrying out routine 200 included herein may beexecuted by a controller, such as controller 12 of FIG. 1, based oninstructions stored on a memory of the controller and in conjunctionwith signals received from sensors of the engine system, such as thesensors described above with reference to FIG. 1. The controller mayemploy engine actuators of the engine system, such as the actuators ofFIG. 1 to adjust engine operation and mitigate the abnormal combustionevents, according to the routines described below.

At 201, routine 200 estimates and/or measures existing engine operatingconditions. Engine operating conditions may include engine speed, engineload, torque demand, air-fuel ratio, manifold absolute pressure (MAP),mass air flow, engine temperature, etc. For example, engine speed may beestimated based on output from the crankshaft acceleration sensor, suchas Hall effect sensor 120 of FIG. 1. Next, at 202, routine 200determines if pre-ignition determination conditions are met. In oneexample, pre-ignition determination conditions may be confirmed inresponse to engine load being higher than a load threshold. As such,pre-ignition events may not occur when the engine is operating at a loadlower than the load threshold. Further, abnormal combustion events atlower engine loads may be due to knock. Thus, if pre-ignitiondetermination conditions are not met at 202, routine 200 continues to203 to assess the presence of knock. Knock sensor output in a knockwindow may be examined and may be compared to a first threshold todetect the presence of knock. Further, the controller may also determinethat abnormal combustion events, if present, are not due topre-ignition. Routine 200 may then end.

Thus, abnormal events at lower engine loads (such as lower than the loadthreshold) may be correlated to knock and not to pre-ignition.

If, however, pre-ignition determination conditions are met at 202 (e.g.,engine load is higher than the load threshold), routine 200 continues to204. When engine load is higher than the load threshold, abnormalcombustion events may be due to one of knock, LSPI, and HSPI. At 204,routine 200 determines if engine speed is higher than a threshold (e.g.,a threshold speed). In one example, the threshold may be 4000 RPM. Inanother example, the threshold may be 4500 RPM. If the engine speed islower than the threshold, abnormal combustion events in the engine maybe attributed to LSPI and/or knock. In addition to determining that theexisting engine speed is either higher or lower than the threshold,routine 200 also relies on output from the knock sensor to identifyLSPI, knock, and HSPI.

If it is determined at 204 that engine speed is lower than thethreshold, routine 200 continues to 206 to receive output from the knocksensor for each of a pre-ignition window and a knock window. Further,output from the knock sensor may be received for each cylinder of anengine in a common engine cycle. As mentioned earlier, the pre-ignitionwindow may occur at an earlier time during the common engine cycle for agiven cylinder relative to the knock window. In addition, the output ofany signals generated by the knock sensor outside the defined windows(e.g., pre-ignition window, knock window) may be disregarded.

Next, at 208, output from the knock sensor for a given knock window iscompared to first threshold, Threshold_KN. Specifically, routine 200confirms if knock sensor output for the given knock window is higherthan the first threshold. The first threshold may be based on alikelihood of cylinder knock, for example. Output from the knock sensorgenerated in the knock window may be processed in different ways, e.g.,amplified, band-pass filtered, rectified, and integrated. In oneexample, output intensity for the knock window may be determined, asdescribed earlier in reference to FIG. 5A, by aggregating knock sensoroutput in the knock window. This output intensity in the knock window(or knock intensity) may be compared to the first threshold. In anotherexample, a frequency of the knock sensor output may be determined andcompared to the first threshold. In yet another example, an amplitude ofthe sensor output may be utilized to detect the presence of knock.

If it is determined that the output of the knock sensor is higher thanthe first threshold, routine 200 continues to 210 to indicate thepresence of knock. Additionally, a knock counter may be incremented totrack a number of knock events (e.g., a knock count) that have occurredover the current drive cycle. The knock count may be stored in acylinder-specific manner and may include the knock count for eachcylinder over the drive cycle, as well as the knock count of the engineover the drive cycle.

Further, at 212, mitigating actions for knock are implemented. As such,knock may be controlled by adjusting spark timing and/or enablingexhaust gas recirculation (EGR) flow. Accordingly, in response to theindication of knock, spark timing is retarded at 214. For example, thecontroller may refer a look-up table stored as a function of knocksensor output relative to engine speed to determine the amount of sparkretard to be applied. Additionally or alternatively, EGR flow is enabledat 214. Herein, an electromechanical actuator coupled to the EGR valvemay receive a signal from the controller to open the EGR valve (e.g.,from closed) and initiate EGR flow. If recirculation of exhaust gasesinto the engine is already occurring, a flow rate of the EGR may beincreased at 214. For example, an opening of the EGR valve may beincreased to increase the flow rate of EGR. The increase in EGR flow mayhowever be regulated based on preserving combustion stability. Forexample, the EGR flow may not be increased if a tip-out condition tolower loads is occurring. In one example, the EGR flow includes cooledlow pressure EGR flow. In another example, the EGR flow includes cooledhigh-pressure EGR flow, or a combination of LP-EGR and HP-EGR flow.Routine 200 then ends.

The amount of spark retard or increase in EGR applied in response to theindication of knock may be adjusted based on the knock count. Forexample, as the knock count (of the cylinder, or the engine) increases(e.g., increases beyond a threshold count), a larger degree of sparkretard may be applied and/or EGR may be increased by a larger amount toreduce the likelihood of further knock events in the affected cylinder.The amount of spark retard applied may be further adjusted based on anamount of EGR that is enabled. For example, less spark retard may beapplied if an amount of LP-EGR is enabled. It will be appreciated thatretarding spark timing may be an initial (e.g., first) action inresponse to knock. As such, spark retard may provide a more immediatemitigating effect on knock. Enabling or increasing EGR flow may followthe spark retard because EGR flow may have a slower mitigating effect onknock.

Returning to 208, if it is determined that output from the knock sensorin the given knock window is not higher than the first threshold,routine 200 continues to 216 to determine if output from the knocksensor in a given pre-ignition window is higher than a second threshold,Threshold_PI. As such, second threshold, Threshold_PI may be higher thanthe first threshold, Threshold_KN. Output from the knock sensorgenerated in the given pre-ignition window may be processed in differentways. For example, signals from the knock sensor generated in thepre-ignition window may be amplified, rectified, band pass filtered,integrated, etc. In one example, similar to that described at 208,output intensity for the pre-ignition window (also termed, pre-ignitionintensity) may be determined by aggregating knock sensor output in thepre-ignition window and may be compared to the second threshold. Inanother example, a frequency of knock sensor signals in the pre-ignitionwindow may be determined via processing. This frequency may be comparedto the second threshold, Threshold_PI. Frequency as used hereinindicates a number of recurring events, or a number of recurring knocksensor output peaks. In yet another example, average amplitude of thesensor output in the pre-ignition window may be determined and comparedto the second threshold.

If the output of the knock sensor in the given pre-ignition window ishigher than Threshold_PI, routine 200 progresses to 218 to indicate thepresence of LSPI. Further, a LSPI counter may be incremented to track anumber of LSPI events (low speed pre-ignition count) that have occurredover the current drive cycle. As such, the pre-ignition count maydetermine a severity of pre-ignition mitigating actions applied. Forexample, as the low speed pre-ignition count increases (or exceeds athreshold count), the severity of the applied mitigating action may beincreased.

Next, at 220 mitigating actions to counter LSPI are applied. Examplemitigating actions may include enriching an affected cylinder, limitingan engine load by reducing air flow into the engine, etc. For example,when alleviating LSPI in an affected cylinder, a degree of enrichmentprovided to the affected cylinder may be based upon the pre-ignitioncount. In another example, the pre-ignition count may determine the loadclip applied to the engine, the load clip affecting a degree of intakethrottle closing. The amount of enrichment or load clip applied inresponse to the indication of LSPI may be adjusted based on the LSPIcount. For example, as the LSPI count (of the cylinder, or the engine)increases (e.g., increases beyond a threshold count), a degree ofrichness of the enrichment may be increased and/or one or moreunaffected cylinders may be enriched in addition to the LSPI affectedcylinder. Likewise, an engine load clip may be increased by reducingintake air flow by a larger amount (e.g., by moving the intake throttlefurther towards a closed position). Engine load may also be limited byreducing boost levels, such as via adjustments to a wastegate or acompressor bypass valve. Mitigating actions for LSPI will be furtherelaborated in FIG. 3. If the output of the knock sensor in the givenpre-ignition window is lower than the second threshold, Threshold_PI,routine 200 continues to 222 to indicate that the engine is operatingwithout LSPI or knock. Routine 200 then ends.

Thus, when pre-ignition determination conditions are met (e.g., engineload is higher than threshold load), and engine speed is lower than thethreshold, routine 200 differentiates between knock and LSPI (206-222).

Returning to 204, if the engine speed is determined to be higher thanthe threshold, routine 200 proceeds to 224 to receive output generatedby the knock sensor in a knock window over a first number of enginecycles and in a pre-ignition window over a second number of enginecycles. In one example, the first number of engine cycles may be thesame as the second number of engine cycles. Further, the first number ofengine cycles and second number of engine cycles may be a common set ofengine cycles. In other words, output from the knock sensor may bereceived for each of the knock window and the pre-ignition window overthe same engine cycles. In another example, the first number of enginecycles may be different and distinct from the second number of enginecycles. In yet another example, a portion of the first number of enginecycles may be common to the second number of engine cycles (that is,they may partially overlap).

In one example, an engine cycle may include two revolutions of thecrankshaft of the engine. Herein, a single engine cycle may beequivalent to one cylinder cycle for a single cylinder of the engine. Toelaborate, the engine cycle includes 720 degrees of crank rotation.During the 720 degrees of crank rotation, a single cylinder of theengine may undergo one cylinder cycle which includes four strokes: anintake stroke, a compression stroke, an expansion stroke, and an exhauststroke. Further, during the same 720 degrees of crank rotation allcylinders of the engine may complete the four strokes. In anotherexample, an engine cycle may include one revolution of the crankshaft ofthe engine. Herein, a single cylinder of the engine may complete twostrokes within the engine cycle (e.g., 360 degrees of crank rotation).

Next, at 226, for each cylinder, the output from the sensor in the knockwindow is integrated over the first number of engine cycles while outputfrom the knock sensor in the pre-ignition window is integrated over thesecond number of engine cycles. Specifically, output intensities in theknock windows for each cylinder may be integrated for the first numberof engine cycles. Likewise, output intensities in the pre-ignitionwindows for each cylinder may be integrated for the second number ofengine cycles. As described earlier in reference to FIGS. 5A and 5B,output intensity of a window may be obtained by integrating knock sensoroutput within the window. Additionally, peak values of the knock sensoroutput within each window may be monitored. To elaborate, peak values ofthe sensor output within each knock window may be examined over each ofthe first number of engine cycles. Similarly, peak values of the outputfrom the knock sensor within each pre-ignition window may be evaluatedover each of the second number of engine cycles. As described earlier inreference to FIGS. 5A and 5B, peak values of knock sensor output may bea height of peaks in the knock sensor output within a given window.Further, peak value in a given window may indicate a highest (e.g.,maximum) peak value within the given window.

At 228, HSPI is indicated based on one or more of integrated knocksensor output and peak values in the windows over the plurality ofengine cycles. For example, integrated knock sensor output (in otherwords, integrated output intensities) for knock windows over the firstnumber of engine cycles may be analyzed. Similarly, integrated knocksensor output for pre-ignition windows over the second number of enginecycles may be monitored. Specifically, the integrated output intensitiesfor knock windows over the first number of cycles may be contrasted to athird threshold while integrated knock sensor output for pre-ignitionwindows over the second number of engine cycles may be compared to afourth threshold. The fourth threshold may be higher than the thirdthreshold. Additionally, peak values in the knock windows may becompared with each other as well as with peak values of the pre-ignitionwindows over the first and second number of engine cycles. Details ofthe process to identify HSPI will be further elaborated in reference toFIGS. 6 and 7 below. As described earlier in reference to FIGS. 5A and5B, the above mentioned comparisons of integrated knock sensor outputand peak values may be performed for overlapping as well asnon-overlapping knock and pre-ignition windows.

Next, at 230, if HSPI is indicated, various mitigating actions areperformed which will be detailed in routine 300 of FIG. 3. For example,HSPI may be alleviated at least partially by selectively deactivatingfuel to an affected cylinder. Further still, engine load may be limited.Routine 200 then ends. Thus, when pre-ignition determination conditionsare met (e.g., engine load is higher than threshold load), and enginespeed is higher than the threshold speed, routine 200 may correlateabnormal combustion events (especially, a transition of combustion eventinitiation from later timings to earlier timings in an engine cycle) toHSPI. Specifically, a comparison of engine speed to the speed thresholdmay differentiate HSPI and LSPI (and knock at lower speeds).

In this way, a controller may differentiate between abnormal combustionevents due to HSPI, LSPI, and knock. Knock and LSPI may be ascertainedbased on a combination of engine speed being lower than the thresholdspeed, engine load higher than the load threshold, and sensor outputfrom an individual knock window and an individual pre-ignition window.For example, LSPI and knock may be detected based on a single enginecycle. Further, knock may be confirmed when knock sensor output in theknock window is compared to a first, lower threshold while LSPI may beindicated in response to knock sensor output in the pre-ignition windowbeing higher than a second, higher threshold. On the other hand, HSPImay be identified based on a combination of engine speed being higherthan the threshold speed, engine load being higher than a thresholdload, and integrated sensor output from a plurality of knock windows andpre-ignition windows over a duration of multiple engine cycles. Inresponse to the identification of these abnormal combustion events,specific actions may be initiated allowing rapid alleviation of theseissues. Mitigating actions to relieve LSPI versus those to reduce HSPIwill be elaborated in FIG. 3.

Turning now to FIG. 6, an example routine 600 is presented for detectingpresence of HSPI based on knock sensor output in non-overlappingpre-ignition and knock windows. Specifically, HSPI may be recognized byintegrating knock sensor output in knock and pre-ignition windows over aplurality of engine cycles and by evaluating peak values within theknock and pre-ignition windows over the plurality of engine cycles.Routine 600 will be described in relation to the engine system shown inFIG. 1 and example knock and pre-ignition windows in FIGS. 4 and 5A, butit should be understood that similar routines may be used with othersystems without departing from the scope of this disclosure.Instructions for carrying out routine 600 included herein may beexecuted by a controller, such as controller 12 of FIG. 1, based oninstructions stored on a memory of the controller and in conjunctionwith signals received from sensors of the engine system, such as thesensors described above with reference to FIG. 1.

Routine 600 depicts the indication of HSPI based on two methods that mayoccur in parallel. As such, routine 600 may be activated whileperforming routine 200 of FIG. 2 (e.g., at 228). As will be elaboratedbelow, the controller may be configured to detect HSPI based onintegrated knock sensor output over multiple knock and pre-ignitionwindows (at 602-614) and peak values of knock sensor output in multipleknock and pre-ignition windows (at 616-624) concurrently.

At 602, routine 600 includes receiving integrated sensor output in knockwindows over the first number of engine cycles for a given cylinder.Specifically, output intensity (e.g., integrated knock sensor outputwithin a given window over a single engine cycle) in knock windows maybe integrated over the first number of engine cycles. As such, anintegrated sensor output in knock windows over the first number ofengine cycles, IKO_Knk, may be determined. It will be noted that IKO_Knkmay also be termed integrated output intensity for knock. Next, at 604,this integrated sensor output in knock windows over the first number ofengine cycles is compared to a third threshold, Thr_3. Specifically,routine 600 determines if IKO_Knk is higher than the third threshold at604. Thus, knock sensor output in knock windows of the first number ofengine cycles may be integrated and compared to the third threshold.

If HSPI is present, abnormal combustion events of higher intensity (e.g.amplitude) may occur at a higher frequency (e.g., a number of recurringevents) in knock windows during earlier engine cycles. The higherintensity and higher frequency of these events may provide an integratedsensor output in the knock windows that increases over the first numberof engine cycles until it is higher than the third threshold. If IKO_Knkis not higher than the third threshold, routine 600 proceeds to 606 toindicate that HSPI is absent. Further, routine 600 returns to 602 tocontinue receiving integrated sensor output for knock windows oversubsequent engine cycles.

However, if it is determined at 604 that IKO_Knk is higher than thethird threshold, routine 600 continues to 608 to receive integratedsensor output from pre-ignition windows for the given cylinder over thesecond number of engine cycles. HSPI may be indicated based on sensoroutput in both knock and pre-ignition windows over the plurality ofengine cycles. Accordingly, after determining that integrated sensoroutput in knock windows over the first number of engine cycles is higherthan the third threshold, the controller also receives integrated sensoroutput for pre-ignition windows (IKO_PI) over the plurality of enginecycles (e.g., second number of engine cycles) at 608. Specifically,output intensity in pre-ignition windows may be integrated over thesecond number of engine cycles to generate IKO_PI, also termedintegrated output intensity for pre-ignition. It will be noted thatknock sensor output in pre-ignition windows may be integrated over thesecond number of engine cycles only after the integrated sensor outputin knock windows over the first number of engine cycles exceeds thethird threshold.

Next, at 610, routine 600 determines if the integrated sensor output inpre-ignition windows over the second number of engine cycles is higherthan a fourth threshold, Thr_4. If HSPI is present, abnormal combustionevents initially occurring in knock windows during earlier engine cyclesmay gradually transition to pre-ignition windows during later enginecycles. Thus, abnormal combustion events may increase in intensity andfrequency in pre-ignition windows during later engine cycles. Inresponse to the rise in intensity and frequency of abnormal combustionevents in pre-ignition windows, the integrated sensor output inpre-ignition windows may increase over the second number of enginecycles until it is higher than the fourth threshold.

In one example, the fourth threshold (Thr_4) may be higher than thethird threshold (Thr_3) for integrated sensor output in knock windowsover the first number of engine cycles. Further still, the fourththreshold for determining HSPI may be different from the secondthreshold, Threshold_PI, for determining LSPI. Likewise, the thirdthreshold, Thr_3 may be distinct from each of the first threshold,Threshold_KN, for determining knock and the second threshold,Threshold_PI for determining LSPI. In another example, the fourththreshold (Thr_4) may be the same as the third threshold, Thr_3.

It will also be appreciated that the second number of engine cycles thatsensor output for pre-ignition windows is integrated over may be basedupon a specific duration subsequent to establishing that IKO_Knk ishigher than the third threshold. HSPI may be indicated only in responseto the integrated knock sensor output in pre-ignition windows increasingto higher than the fourth threshold within the second number of enginecycles.

If it is confirmed at 610 that IKO_PI is not higher than the fourththreshold, routine 600 progresses to 622 to indicate that HSPI isabsent. However, HSPI may likely occur and the controller may continueto monitor the integrated sensor output in pre-ignition windows oversubsequent engine cycles. Routine 600 then ends. If however it isdetermined that IKO_PI is higher than the fourth threshold, routine 600continues to 612 where it may optionally confirm if spark retard for thegiven cylinder is higher than a threshold spark retard, Ts.

Spark timing may be retarded to mitigate knock which may be detectedbased on increased abnormal combustion events in knock windows. As such,knock may occur at higher engine speeds and may be alleviated byretarding spark timing. The likelihood of HSPI may be higher if thespark timing is retarded by a higher degree (e.g., a maximum retardclip) in combination with integrated knock sensor output in knockwindows exceeding the third threshold over the first number of enginecycles and integrated sensor output in pre-ignition windows exceedingthe fourth threshold over the second number of engine cycles. In otherwords, the simultaneous presence of increased knock intensity and sparkretard at the maximum clip may indicate that spark from the spark plugis no longer the ignition source and an alternate source of ignition ispresent. Accordingly, it may be determined that HSPI may be occurring.

Thus, if it is determined that spark retard in the given cylinder ishigher than the threshold spark retard, routine 600 continues to 614 toindicate HSPI. Thus, HSPI may be indicated responsive to an increase inthe integrated output in the pre-ignition window following theintegrated output in the knock window exceeding a threshold (e.g.,Thr_3) and spark timing in the cylinder being retarded by a thresholdamount (e.g., Ts). Routine 600 may alternatively proceed to 614 directlyfrom 610 and indicate the presence of HSPI based upon the integratedsensor output in pre-ignition windows over the second number of enginecycles surpassing the fourth threshold at 610. As such, the controllermay respond to the indication of HSPI via various remedial actions suchas those described at 316 of routine 300.

In parallel to the above, at 616, routine 600 receives peak values ofsensor output in each knock window (PK_Knk) of the first number ofengine cycles. The peak values may, in one example, be a value of thehighest peak (e.g., height of the peak) in the knock sensor outputwithin each knock window. In another example, peak value may be theaverage value of heights of all peaks in the knock sensor output withineach knock window. These peak values for each knock window may becompared over the first number of engine cycles. Next, at 618 routine600 receives peak values of sensor output in each pre-ignition window(PK_PI) of the second number of engine cycles. In one example, the peakvalues may be a value of the highest peak (e.g., height of the peak) inthe knock sensor output within each pre-ignition window. In anotherexample, peak value may be the average value of heights of all peaks inthe knock sensor output within each pre-ignition window. Peak values foreach pre-ignition window may be compared over the second number ofengine cycles. Further, peak values for the pre-ignition windows in thesecond number of engine cycles may be compared with peak values forknock windows in the first number of engine cycles.

At 620, routine 600 determines if peak values in the knock windowsdecrease over the first number of engine cycles with an increase in peakvalues in the pre-ignition windows over the second number of enginecycles. In one example, the increase in peak values in the pre-ignitionwindows may follow the decrease in peak values in the knock windows. Inanother example, the rise in peak values in the pre-ignition windows maybe concurrent to the decline in peak values in the knock windows. Ifyes, routine 600 proceeds to 624 to indicate the presence of HSPI. Onthe other hand, if it is determined that peak values in the knockwindows are not decreasing and/or peak values in the pre-ignitionwindows are not increasing, routine 600 continues to 622 to indicatethat HSPI is absent. As such, routine 600 may continue to monitor knocksensor output in knock and pre-ignition windows for detecting HSPI.

In addition to receiving peak values in knock sensor output in the knockand pre-ignition windows over the plurality of engine cycles, thecontroller may also monitor a rate of change in knock sensor outputwithin each knock and pre-ignition window. For example, the rate ofchange in sensor output may include a frequency of the output. Frequencyherein implies an incidence or a number of recurring events. In anotherexample, the rate of change may include an amplitude of the output.Herein, HSPI may be indicated in response to a decrease in frequencyand/or amplitude of sensor output in knock windows over the first numberof engine cycles and an increase in frequency and/or amplitude of sensoroutput in pre-ignition windows over the second number of engine cycles.For example, the decrease in frequency and/or amplitude of sensor outputin knock windows may precede the increase in frequency and/or amplitudeof sensor output in pre-ignition windows. In another example, thedecrease in frequency and/or amplitude of sensor output in knock windowsmay occur simultaneously with the increase in frequency and/or amplitudeof sensor output in pre-ignition windows.

FIG. 7 depicts an example routine 700 for detecting HSPI events based onknock sensor output in overlapping knock and pre-ignition windows.Specifically, the routine includes comparing and contrasting knocksensor output in a plurality of segments in pre-ignition windows.Routine 700 will be described in relation to the engine system shown inFIG. 1 and example knock and pre-ignition windows in FIGS. 4 and 5B, butit should be understood that similar routines may be used with othersystems without departing from the scope of this disclosure.Instructions for carrying out routine 700 included herein may beexecuted by a controller, such as controller 12 of FIG. 1, based oninstructions stored on a memory of the controller and in conjunctionwith signals received from sensors of the engine system, such as thesensors described above with reference to FIG. 1.

At 702, routine 700 receives output from a knock sensor for a pluralityof overlapping knock and pre-ignition windows for a given cylinder.Specifically, knock sensor output may be received for knock andpre-ignition windows in a third number of engine cycles. As an example,the third number of engine cycles may be a combination of the firstnumber of engine cycles and the second number of engine cycles. Inanother example, the third number of engine cycles may be the same aseither the first number of engine cycles or the second number of enginecycles. In yet another example, the third number of engine cycles may bedifferent and distinct from each of the first and the second number ofengine cycles.

At 704, routine 700 divides at least the pre-ignition window in eachengine cycle into a plurality of segments (as shown in map 450 of FIG.4, and described in reference to FIG. 5B). As such, at 705, the numberof segments that each pre-ignition window is divided into depends on adegree of overlap between the pre-ignition window and the knock windowin each engine cycle. For example, if the degree of overlap is higher,the pre-ignition windows may be split into a higher number of segments.Contrarily, if the amount of overlap between the knock and pre-ignitionwindow is smaller, the pre-ignition window may be split into fewersegments. Further, the number of segments that the pre-ignition windowis divided into may also vary with an increase in the number of enginecycles. The plurality of segments that the pre-ignition window is splitinto may additionally or optionally be based upon existing engineconditions such as engine speed (Ne), engine load, spark timing, etc.For example, the pre-ignition window may be split into a higher numberof segments if the engine speed is higher. In alternate examples, theknock window may be divided into segments instead of splitting thepre-ignition window.

In yet another example, the number of segments that the pre-ignitionwindow is split into may also be based upon the first threshold(Threshold_KN) and the second threshold (Threshold_PI). For example, ifthe first threshold and the second threshold are close to each other,the pre-ignition window may be split into a higher number of segments.In another example, if the first threshold and the second threshold areseparated by a wider margin, the pre-ignition window may be divided intofewer segments.

Routine 700 then proceeds to 706 to integrate sensor output in each ofthe plurality of segments over the third number of engine cycles.Accordingly, an integrated sensor output (IKO) or output intensity isgenerated for each of the plurality of segments over the third number ofengine cycles. Further, at 708, routine 700 determines if a sum of theintegrated sensor output (IKO) of the plurality of segments in a givenengine cycle is higher than the second threshold, Threshold_PI. If no,routine 700 continues to 710 to indicate that pre-ignition is absent.Routine 700 then ends. If, on the other hand, the sum of integratedsensor output in the plurality of segments for the given engine cycle ishigher than Threshold_PI, routine 700 progresses to 712 to indicate alikelihood of pre-ignition.

Routine 700 then proceeds to confirm the presence of HSPI by one or bothof methods described earlier in reference to FIG. 6. As in routine 600,the controller may be configured to detect HSPI based on integratedknock sensor output over multiple segments in pre-ignition windows (at714-718) and peak values of knock sensor output in multiple segments ofpre-ignition windows (at 720-726) concurrently.

At 714, routine 700 includes analyzing integrated sensor output in eachsegment of the plurality of pre-ignition windows over the third numberof engine cycles. As shown in map 550 of FIG. 5B, sensor output in eachsegment (e.g., first segment 501, second segment 503, third segment 505)of each pre-ignition window may be integrated to generate an integratedsensor output such as IKO_Seg1, IKO_Seg2, etc. Next, at 716, routine 700assesses whether integrated sensor output (IKO) in later segments isdecreasing while integrated sensor output in earlier segments isincreasing over the third number of engine cycles. Referring to FIG. 5B,it may be determined if IKO in third segment 505 (e.g., a later segment)decreases from engine cycle ‘p’ to engine cycle ‘p+1’. At the same time,the controller may determine if IKO in earlier segments, such as firstsegment 501, is increasing from engine cycle ‘p’ to engine cycle ‘p+1’.

Thus, the comparison of IKO in the multiple segments of the pre-ignitionwindows over the plurality of engine cycles includes examining anadvancing of IKO from later segments to earlier segments over theplurality of engine cycles. To elaborate, IKO in later segments may behigher than those in earlier segments for each pre-ignition windowinitially, such as during an earlier portion of the plurality of enginecycles. As the engine cycles continue to occur, IKO in later segmentsmay gradually decrease while IKO in earlier segments within thecorresponding pre-ignition windows increases. This transition of higherIKO from later segments in a segmented pre-ignition window to a higherIKO in earlier segments of the segmented pre-ignition window mayindicate earlier initiation of combustion and, thereby indicate HSPI.

In another example, the IKO in each segment may be compared to athreshold, such as fourth threshold (Thr_4) to determine the presence ofHSPI. The IKO in each segment may be compared to the same threshold,such as the fourth threshold. HSPI may be indicated based on the IKO oflater segments being higher than the fourth threshold during the earlierportion of the plurality of engine cycles, followed by a decrease in IKOof later segments to lower than the fourth threshold in the laterportion of the plurality of engine cycles. At the same, the IKO ofearlier segments during the earlier portion of the plurality of enginecycles may be lower than the fourth threshold but may increasesubsequently to higher than the fourth threshold during the laterportion of the plurality of engine cycles.

If it is confirmed that IKO is not decreasing in the later segmentsand/or IKO is not increasing in the earlier segments, routine 700continues to 724 to indicate that the likelihood of HSPI is lower.However, if the IKO is increasing in earlier segments whilesimultaneously decreasing in later segments over the third number ofengine cycles, routine 700 progresses to 718 to indicate the presence ofHSPI. Routine 700 then ends.

In parallel to the above, at 720 routine 700 receives and monitors peakvalues of sensor output (PK) in each of the plurality of segments overthe third number of engine cycles. As shown in map 550 of FIG. 5B, peakvalues of sensor output in each segment (e.g., first segment 501, secondsegment 503, third segment 505) of each pre-ignition window may beevaluated. Peak values, as explained earlier, may include a height ofthe highest peak in the knock sensor output within a segment of a givenpre-ignition window. Alternatively, peak value may be an average of theheights of all peaks within the segment of the given pre-ignitionwindow. Next, at 722, routine 700 determines if peak values aretransitioning from later segments to earlier segments over the thirdnumber of engine cycles.

If HSPI is present, peak values in later segments may be higherinitially than corresponding peak values in earlier segments.Specifically, peak values in later segments may be higher during anearlier number of the plurality of engine cycles. Further, as the numberof engine cycles increases, peak values in the later segments mayundergo a gradual decrease while peak values in the earlier segments ofthe same pre-ignition windows experience a gradual increaseconcurrently. Thus, in one example, highest peak values may advance fromlater segments to earlier segments over the course of the third numberof engine cycles indicating an advancement of initiation of combustionin the engine cycle.

Therefore, if it is confirmed that peak values are transitioning fromlater segments to earlier segments over the third number of enginecycles, routine 700 proceeds to 726 to indicate presence of HSPI. On theother hand, if peak values are not transitioning from later segments toearlier segments, routine 700 proceeds to 724 to indicate that thelikelihood of HSPI is lower. Routine 700 then ends.

In this manner, abnormal combustion events may be categorized as HSPIevents based on evaluation of knock sensor output in overlapping as wellas non-overlapping knock and pre-ignition windows over a plurality ofengine cycles. HSPI may be more accurately identified based on knocksensor output by using one or both methods described above enabling aspecific mitigating action. Further, by identifying HSPI and applyingdesired remedies, a likelihood of runaway pre-ignition may be reduced.

FIG. 3 includes an example routine 300 illustrating distinct mitigatingactions for LSPI and HSPI. As such, routine 300 will be described inrelation to the engine system shown in FIG. 1, but it should beunderstood that similar routines may be used with other systems withoutdeparting from the scope of this disclosure. Instructions for carryingout routine 300 included herein may be executed by a controller, such ascontroller 12 of FIG. 1, based on instructions stored on a memory of thecontroller and in conjunction with signals received from sensors of theengine system, such as the sensors described above with reference toFIG. 1. The controller may employ engine actuators of the engine system,such as the actuators of FIG. 1 to adjust engine operation and performmitigating actions, according to the routines described below.

At 302, routine 300 determines if LSPI is detected. As described earlierin reference to 218 of routine 200, LSPI may be indicated based onengine speed being lower than the threshold as well as sensor output inthe pre-ignition window being higher than Threshold_PI. If LSPI isdetected, routine 300 moves to 304 to initiate mitigating actions forLSPI. Therein, in response to an indication of LSPI, the controllerenriches the affected cylinder(s) for a first number of combustionevents. The enriching may include increasing a degree of richness ofcylinder enrichment. For example, an amount of fuel injection deliveredvia a direct and/or port injector into the affected cylinder(s) may beincreased to operate the cylinder richer than stoichiometry, at thedetermined enrichment level, for one or more engine cycles. Herein, thecontroller may communicate a signal to fuel injector(s) coupled to theaffected cylinder(s) to increase fueling of the correspondingcylinder(s), e.g., by increasing a pulse width of the fuel injector(s).In addition, a number of injections via which the fuel is delivered maybe increased. For example, the fuel may be delivered as multiple intakestroke injections or multiple compression stroke injections, or acombination thereof. Further still, a timing of the injection may beadjusted. For example, a portion of the fuel may be delivered in theintake stroke while a remaining portion of the fuel may be delivered ina compression stroke of the cylinder while varying (e.g., advancing orretarding) an overall fuel injection timing.

The affected cylinder(s) may be enriched for a specific number ofcombustion events (e.g., a first number of enriched combustion events).The number of combustion events that the affected cylinder is enrichedfor may depend, in one example, on an intensity of LSPI.

Further still, the degree of enrichment as well the number of combustionevents for which the cylinder is enriched may be adjusted based on thepre-ignition count of the cylinder (and/or of the engine). For example,as the pre-ignition count increases, the number of cylinder enrichmentevents and the degree of richness may be increased. In addition,cylinder enrichment may be extended to one or more pre-ignitionunaffected cylinders so as to pre-empt pre-ignition being induced in theunaffected cylinders.

In addition to enriching the affected cylinder, a limit or clip isapplied to engine load to mitigate the LSPI. Specifically, a firstamount of load limit may be applied on the engine for a first duration.By limiting the engine load, however, torque production may betransiently reduced. As used herein, limiting the engine load mayinclude limiting air flow into one or more cylinders of the engine.Intake air flow may be reduced by one or more of reducing an opening ofan intake throttle, adjusting a cylinder valve timing to reduce anintake aircharge, and increasing an opening of a wastegate coupledacross the exhaust turbine. For example, a control signal may be sentfrom the controller to an electromechanical actuator coupled to athrottle plate of the intake throttle. Specifically, theelectromechanical actuator may rotate the throttle plate of the intakethrottle to a more closed position from a more open position to reduceintake air flow. The controller may also communicate with the camactuation systems to adjust valve timings of the affected cylinders toreduce intake air charge. As an example, a duration of intake valveopening may be decreased by adjusting valve timings. Alternatively, thecontroller may provide a signal to an electromechanical actuator coupledto the wastegate to adjust the wastegate to a more open position from amore closed position to increase exhaust bypass flow and reduce boostpressure, thereby limiting engine load.

The first load limit may be applied for a first duration such as aspecific number of combustion events, a certain number of engine cycles,a duration of time, etc. Further, the first load limit as well thenumber of engine cycles for which the engine load is limited may beadjusted based on the pre-ignition count of the cylinder (and/or of theengine). For example, as the pre-ignition count increases, intake airflow may be further reduced, and the engine load may be lowered further.In addition, load limiting may be applied for a larger number of enginecycles.

Next, at 306, routine 300 adjusts the mitigating actions based on acount of LSPI events. For example, if the LSPI count is higher than athreshold number, a degree of cylinder enrichment may be increased.Additionally, the first amount of load limiting may be increased.Further still, if LSPI is not alleviated within the first number ofcombustion events, the controller commences enriching cylindersunaffected by LSPI at 308. Thus, cylinders that do not experience LSPImay also receive an increased degree of cylinder enrichment. Inaddition, at 310, based on the LSPI count increasing to higher than thethreshold number, the load limit is maintained active and “latched”until an engine-on/off cycle or key-on/off cycle is confirmed. As such,when load limiting is applied to the engine, engine power may bereduced. Thus, when applying the more restrictive load limit, anassociated warning may be delivered to the vehicle operator to warn themof the reduced power state. Accordingly, a malfunction indicator lamp(MIL) may be activated when the load limit is latched and a diagnostictrouble code (DTC) may be enabled.

Returning to 302, if it is determined that LSPI is not detected, routine300 continues to 312 to confirm if HSPI is indicated. As mentionedearlier in routine 200, HSPI may be identified based on a combination ofengine speed being higher than a threshold (e.g., a speed threshold),engine load being higher than a load threshold, and integrated knocksensor output and/or peak values in pre-ignition and knock windows overmultiple engine cycles. If HSPI is not detected, routine 300 continuesto 314 to indicate that abnormal combustion events are not detected andthe engine is operating without either LSPI or HSPI. Routine 300 thenends. However, if HSPI is confirmed at 312, routine 300 progresses to316 to initiate mitigating actions for HSPI.

For example, HSPI may be alleviated by ceasing fuel supply to theaffected cylinder(s) for a second number of combustion events. Herein,fuel injection into the affected cylinder(s) via the direct and/or portinjector may be stopped. The controller may communicate a signal to fuelinjector(s) coupled to the affected cylinder(s) to cease fueling.

Fuel supply into the affected cylinder(s) may be discontinued for aspecific number of combustion events (e.g., the second number ofcombustion events). As such, fuel supply may be resumed after thecompletion of the second number of combustion events. The second numberof combustion events may depend, in one example, on an intensity ofHSPI. Alternatively, a counter of HSPI events may establish the secondnumber of combustion events. It will be noted that the second number ofcombustion events (that fuel supply to affected cylinders is ceased) maybe distinct from the first number of combustion events that the affectedcylinder is enriched in response to LSPI. For example, the first numberof combustion events that cylinders affected by LSPI receive enrichmentfor may be smaller relative to the second number of combustion eventsthat the cylinders affected by HSPI do not receive fuel supply. In otherwords, HSPI may be mitigated by terminating fuel supply to the affectedcylinder for a larger number of combustion events relative to the numberof combustion events that the cylinder affected by LSPI is enriched.

In addition to discontinuing fuel supply to cylinders affected by HSPI,the engine may also operate with a limited load for a second duration.As such, engine load may be limited by a second amount, the secondamount different and distinct from the first amount of load limitingapplied to remedy LSPI. For example, the second amount of load limit maybe higher than the first amount of load limit. In other words, thesecond amount of load limit applied in response to HSPI may be morerestrictive than the first amount of load limit applied in response toLSPI, and intake air flow may be reduced more in the second load limitas compared to the first load limit. Further still, the second amount ofengine load limit may be applied for a second duration to alleviateHSPI. The second duration may be the second number of combustion events.The second duration may be longer than the duration that the firstamount of load limit applied in response to LSPI. In other words, theengine may be operated with a higher load limit for a longer duration inresponse to HSPI relative to engine operation in response to LSPI.

Engine speed may also be limited in response to indication of HSPI. Forexample, an available maximum engine speed may be clipped when HSPI isdetected. In one example, engine speed may be limited by reducing intakeair flow. In another example, a pulse width of a fuel injector may bereduced.

It will be noted that in response to HSPI being mitigated, fuel supplymay be restored and the engine may be operated without load limits orspeed limits. In another example, engine load limiting may be removedafter the second duration is completed (e.g., after the second number ofcombustion events are concluded) and fuel supply into the affectedcylinder may be restarted. In other words, engine load may be resumedafter HSPI is mitigated. Mitigating actions for HSPI (or LSPI) may alsobe ceased in response to a reduction in engine load. In one example,fuel supply to the HSPI affected cylinder may be restored responsive toa reduction in torque demand (e.g., a tip-out). As such, pre-ignitionevents are less likely when engine load is lower than the thresholdload. Accordingly, a change in engine operating conditions to lowerloads may terminate any ongoing HSPI mitigation actions.

Next, at 318, a severity of the mitigating actions in response to HSPIis adjusted based on a count of HSPI events. For example, if the HSPIcount is higher than a threshold number for HSPI events, the controllerceases fuel supply to at least a portion of cylinders unaffected by HSPIat 320. Thus, cylinders that do not experience HSPI may experiencetermination of fuel supply therein. In another example, the engine maybe operated with a higher amount (e.g., higher than the second amount)of load limiting in response to the HSPI count being higher than thethreshold number of HSPI events.

Further, at 322, in response to multiple recurrences of HSPI (e.g.,higher than the threshold number for HSPI events), the engine load limitis maintained active and “latched” until an engine-on/off cycle orkey-on/off cycle is confirmed. Further still, the MIL may be activatedwhen the load limit is latched and a separate DTC (e.g., distinct fromthat for LSPI) may be enabled.

In this manner, each of LSPI and HSPI may be eased to reduce enginedegradation due to pre-ignition. While LSPI may be alleviated byenriching one or more affected cylinders, HSPI may be moderated byterminating fuel supply to the affected cylinders. As such,discontinuing fuel supply to the affected cylinders may bring about afaster reduction in HSPI. Further, each of LSPI and HSPI may bemitigated by limiting engine loads. However, a higher amount of loadlimiting may be applied to the engine in response to HSPI than that forLSPI. Accordingly, engine torque production may be considerably reducedwhile responding to HSPI events.

Thus, an example method for an engine may comprise indicating low speedpre-ignition based on knock sensor output assessed in each of a knockwindow and a pre-ignition window, and indicating high speed pre-ignitionbased on an integrated knock sensor output, integrated over a number ofengine cycles, in each of the knock window and the pre-ignition window.The method may further comprise, in response to the indication of lowspeed pre-ignition, enriching an affected cylinder and reducing engineintake air flow by a first amount, and in response to the indication ofhigh speed pre-ignition, deactivating fuel to the affected cylinder andreducing engine intake air flow by a second amount, the second amounthigher than the first amount. Further, in response to the indication oflow speed pre-ignition, the affected cylinder may be enriched for afirst, smaller number of combustion events, and wherein in response tothe indication of high speed pre-ignition, fuel may be deactivated inthe affected cylinder for a second, larger number of combustion events.

Now turning to FIG. 8, a schematic block diagram 800 illustrating engineload-limiting adjustments is shown. Limiting of engine loads may bebased on an output of the knock sensor generated in each knock windowand each pre-ignition window over a plurality of engine cycles. Theroutine may start with a feed-forward portion of load limiting 802wherein load limiting is performed in anticipation of pre-ignition(e.g., LSPI, HSPI) and taking into account various other loadrestricting conditions and load demands 804. Specifically, a firstcontroller K1 may determine load limits based on engine operatingconditions, such as based on an engine speed-charge temperaturecondition at 802, and may also determine load limits corresponding toone or more load constraining conditions (or “features”) and loaddemands. These may include, for example, load limits for providingappropriate traction control (e.g., a load limiting responsive to wheelslip), other load demands, etc. The controller may select the lowest ofall the load limits assessed to be a nominal load limit, orTqe_load_limit 806, wherein this lowest load limit is applied inanticipation of pre-ignition.

The load limit may then be clipped with a load clip 808. The load clipmay be based on various factors. In one example, the controller maystart with a nominal load clip that is based on nominal conditions. Thisnominal load clip may be provided (e.g., read from a 2D map) as afunction of engine speed and manifold charge temperature. The load clipmay then be adjusted by a multiplication factor that ranges from −1to 1. The factor may be based on feed-forward measurements such as fueloctane content, fuel ethanol or alcohol content, air-to-fuel ratio,engine LSPI count, and engine HSPI count. Thus, a lean air-to-fuel ratioor a low octane fuel that will make the probability of pre-ignition gohigher results in a load clip wherein the interpolation of the load clipmoves the load limit to a lower value (such as a low effect pre-ignitionmitigation value). In another example, a rich air-to-fuel ratio or ahigh octane content of the fuel may result in a higher load limit (suchas a high effect pre-ignition mitigation value). The torque load limitis then arbitrated with the load clip to determine an arbitrated torqueload limit 810.

The load clip also includes the feedback portion of pre-ignition loadlimiting, wherein the load limit is further adjusted based on a learnedLSPI and HSPI rate or count, as counted by LSPI counter 818 and HSPIcounter 828. The count of LSPI and HSPI events may be determined basedupon knock sensor output in each of a knock window and a pre-ignitionwindow. Specifically, controller K2 receives inputs regarding enginespeed, Ne, and signals from a knock sensor, such as knock sensor 90 ofFIG. 1, and processes these inputs to provide a knock sensor output in apre-ignition window, KO_PI_window 814, and a knock sensor output in aknock window, KO_KNK_window 816. Knock sensor output in each knockwindow and each pre-ignition window is then utilized to detect LSPIevents (based on comparing knock sensor output in a pre-ignition windowwith the second threshold, Threshold_PI) and HSPI events. LSPI counter818 tracks a count of LSPI events and supplies the count to the loadclip at 808. Further, knock sensor output from each knock andpre-ignition window may be fed to each of controller K3 and K4.Controller K3 determines HSPI events based on integrated knock sensoroutput (IKO) in each knock and pre-ignition window at 820 over aplurality of engine cycles. Meanwhile, controller K4 detects HSPI eventsbased on peak values in knock sensor output (PK) in each knock andpre-ignition window at 822. HSPI counter 824 tracks a count of HSPIevents and provides the HSPI count to the load clip at 808.

Once a threshold number of pre-ignition events (whether LSPI or HSPI) isreached, a respective pre-ignition counter may be activated and maystart to determine a pre-ignition rate. Thus, if the LSPI counterestimates that a threshold number of LSPI events is reached, a LSPI rate830 may be determined. On the other hand, if the HSPI counter determinesthat a threshold number of HSPI events is attained, a HSPI rate 826 maybe assessed. If the pre-ignition rate is higher, a respectivepre-ignition load limit may be calculated. For example, if the rate ofLSPI is higher, LSPI_load_limit 834 may be estimated. In anotherexample, if the rate of HSPI is higher, HSPI_load_limit 828 may beevaluated. Thus, the LSPI counter and the HSPI counter may function inparallel with each other.

Controller K5 may then select the desired load limit 838 to be thelowest of these load limits. Thus, the desired load limit may be thelowest of the arbitrated load limit, the LSPI load limit, and the HSPIload limit. As elaborated earlier in reference to FIG. 3, the HSPI loadlimit may be higher (e.g., more restrictive) than the LSPI load limit.

Referring now to FIG. 9, it includes map 900 illustrating an exampledetection and mitigation of LSPI and HSPI using knock sensor output innon-overlapping knock and pre-ignition windows for a single cylinder inan engine. As such, map 900 will be described in relation to the exampleengine system shown in FIG. 1 as well as example sensor output in knockand pre-ignition windows of FIGS. 4 and 5A.

Map 900 depicts a pre-ignition flag at plot 902, an opening of an intakethrottle at plot 904, fueling of the single cylinder at plot 906,integrated knock sensor output (IKO) in a knock window at plot 908,integrated knock sensor output in a pre-ignition (PI) window at plot910, sensor output from a knock sensor in the knock window at plot 912,sensor output in the PI window at plot 914, and engine speed at plot916. Integrated knock sensor output as described earlier includesintegrating sensor output in each knock and each pre-ignition window.Further, plots 908 and 910 represent changes in the integrated knocksensor output as the number of engine cycles increases with time alongthe x-axis. Accordingly, plots 908 and 910 present integrated knocksensor output values for respective knock and pre-ignition windows overmultiple engine cycles. Sensor output in each knock and PI window asshown in plots 912 and 914, respectively, includes an example sensoroutput depicting peaks in the sensor output. Line 907 represents thethird threshold, Thr_3, of routine 600 while line 909 represents thefourth threshold, Thr_4 of routine 600. Line 911, represents the firstthreshold, Threshold_KN, for detecting knock, line 913 represents thesecond threshold, Threshold_PI, for detecting LSPI and line 915represents a threshold speed for determining LSPI and HSPI. All plotsare shown over time, along the x-axis. Further, time increases from theleft of the x-axis towards the right and may also indicate an increasein the number of engine cycles. Note that elements aligning at a commontime on the graph, such as at time t1, for example, are occurringconcurrently, including for example where one parameter is increasingwhile another parameter is decreasing.

At t0, the engine may be operating at a speed lower than the thresholdspeed (line 915) with the opening of the intake throttle at a loweramount. As such, intake air flow entering the engine (and the cylinder)may be lower. Further, the single cylinder may receive a smaller amountof fuel based on the existing engine speed and other engine conditions,as shown by plot 906. Further, the engine may be operating withoutpre-ignition, as depicted by the PI flag (plot 902) and sensor outputsin plots 912 and 914.

At t1, knock sensor output in the pre-ignition window rises above thepre-ignition (second) threshold (line 913). In response to the sensoroutput being higher than the pre-ignition threshold with the engineoperating at lower speeds, the PI flag indicates LSPI at t1. In responseto the indication of LSPI, a controller may enrich the cylinder.Accordingly, fueling of the affected cylinder is increased at t1. In oneexample, fueling of the affected cylinder may be increased by increasinga pulse width of a fuel injector delivering fuel into the affectedcylinder. In addition to enriching the affected cylinder, the controllermay also limit engine loads. Engine load may be limited by reducing theopening of the intake throttle at t1 (plot 904) thereby decreasing theamount of intake air flowing into the engine. Thus, the intake throttlemay be adjusted from a position that is more open to a position that ismore closed.

In response to these mitigating actions, LSPI may subside, as shown bysensor output in the pre-ignition window remaining below thepre-ignition threshold between t1 and t3. At t2, engine speed mayincrease to above the threshold speed (line 915). As an example, enginespeed may rise in response to a sudden increase in operator torquedemand. For example, the vehicle may be ascending an incline. In anotherexample, the vehicle may be accelerating to merge with other vehicles ona highway. In order to produce the desired engine speed, cylinderfueling may be adjusted and the opening of the intake throttle may bealtered. As shown, the cylinder may receive a higher amount of fuelrelative to the amount of fuel received at t0 (at lower engine speeds).Further, the amount of fuel received in response to the increase inengine speed may be lower than that received for cylinder enrichmentresponsive to LSPI. In addition to adjusting the fueling of thecylinder, the opening of the intake throttle may be increasedsignificantly at t2 to enable a higher intake air flow into the engine.

As the engine continues to operate at higher engine speeds, output fromthe knock sensor in each knock window and pre-ignition window may bemonitored. Between t2 and t3, sensor output in the later, knock windowsincludes multiple high peaks while output of the knock sensor in theearlier, pre-ignition windows shows lower peaks (or peak values).Specifically, peak values in the later, knock windows may be higher thanthe knock threshold (line 911) while peak values in the earlier,pre-ignition windows may be lower than the pre-ignition threshold (line913). As such, abnormal combustion events may be observed in later,knock windows.

Sensor output in the knock windows may be integrated over multipleengine cycles to yield the integrated knock sensor output shown in plot908. As shown, integrated knock sensor output in knock windows risesprogressively after t2 and reaches the third threshold (line 907) at t3.For further clarification of the variation in integrated knock sensoroutput, regions 901 and 903 are indicated depicting the increase inintegrated output intensity of knock windows. Specifically, region 901occurs earlier than region 903. Further, area of region 903 is greaterthan area of region 901 since abnormal combustion events are higher(e.g., higher intensity, higher frequency, etc.) in knock windows asengine cycles increase. Further still, as the intensity of abnormalcombustion events in knock windows increases, so does the integratedsensor output in knock windows. In comparison, integrated sensor outputin pre-ignition windows between t2 and t3 is considerably lower.

Once the integrated sensor output in the knock windows reaches the thirdthreshold at t3, the controller may monitor integrated sensor output inpre-ignition windows for a duration ‘D’. As such, duration ‘D’ may be aspecific number of combustion events, a number of engine cycles, etc.Sensor output in the pre-ignition windows after t3 includes an increasein the number of peaks as well as peak values. Consequently, theintegrated sensor output in pre-ignition windows begins to increasesteadily after t3 and attains the fourth threshold (line 909) byduration ‘D’ at t4. For further clarification of the variation inintegrated knock sensor output in the pre-ignition windows after t3,regions 921 and 923 are shown depicting the increase in integratedoutput intensity of pre-ignition windows over a plurality of enginecycles following the rise in integrated knock sensor output.Specifically, area of region 923 is greater than area of region 921indicating that abnormal combustion events are escalating inpre-ignition windows as the number of engine cycles is increasing.Further, area of region 923 is also greater than area of region 903signifying that abnormal combustion events transitioning from knockwindows into pre-ignition windows. Furthermore, the combustion events inpre-ignition windows may be of higher intensity at a higher frequencythan prior to t3. In comparison, integrated sensor output in knockwindows between t3 and t4 begins to decrease. Region 905 under plot 908denotes the reduction in integrated output intensity of the knockwindows as the number of engine cycles increases. Herein, region 905under plot 908 is smaller than region 903. Herein, integrated knocksensor output in knock windows may rise above a threshold (e.g., Thr_3)followed by integrated knock sensor output in pre-ignition windowsrising above a distinct threshold (e.g., Thr_4).

It will also be noted that peak values (e.g., peak heights) in sensoroutput in the knock windows between t2 and t4 are decreasing (asindicated by dashed line 917) while peak values (e.g., peak heights) insensor output in the pre-ignition windows is simultaneously increasing(as indicated by dashed line 919).

Thus, HSPI may be indicated responsive to one or more of an increase inthe integrated output in the knock windows followed by an increase inthe integrated knock sensor output in the pre-ignition windows, and adecrease in a peak value of the output of the knock sensor in the knockwindows with an increase in the peak value of the output of the knocksensor in the pre-ignition windows (while engine speed is higher thanthe threshold, line 915). Accordingly, at t4, the PI flag indicatesHSPI. In response to identification of HSPI, various mitigating actionsmay be initiated. Thus, at t4, fueling of the cylinder is discontinued(plot 906) and engine load may be limited by reducing intake air flowinto the engine. Specifically, intake air flow may be reduced bydecreasing the opening of the intake throttle (plot 904). It will beappreciated that the opening of the intake throttle may be reduced to ahigher degree (T_H) in response to HSPI relative to the decrease inopening of the intake throttle in response to LSPI (T_L). In otherwords, engine load limiting in response to HSPI may be more restrictivethan that for LSPI. The reduction in intake air flow may also limitengine speed. As shown between t4 and t5, engine speed reduces to thatof the threshold speed (or lower) in response to the decrease in intakeair flow.

Between t4 and t5, HSPI may subside in response to the variousmitigating actions as indicated by the reduced peak values, as well asdecrease in integrated knock sensor output, in each of the knock andpre-ignition windows. In one example, the duration between t4 and t5 maybe a pre-determined number of combustion events. Therefore, at t5,actions to alleviate HSPI may be terminated. At t5, fueling of thecylinder may be restored while simultaneously eliminating the limit onengine load. Accordingly, the cylinder may receive fuel at t5, and theopening of the intake throttle may be increased at t5 as the enginereturns to operate at higher engine speeds. Accordingly, the engine mayreceive a higher intake air flow and engine load limiting may be removedin response to mitigation of HSPI.

Thus, LSPI and HSPI may be differentiated based upon engine speed andknock sensor output in knock and pre-ignition windows. Each variety ofpre-ignition may be mitigated using distinct remedial actions.

Referring now to FIG. 10, it includes map 1000 illustrating an exampledetection of HSPI using knock sensor output in overlapping knock andpre-ignition windows for a single cylinder in an engine. As such, map1000 will be described in relation to the example engine system shown inFIG. 1 as well as example sensor output in knock and pre-ignitionwindows of FIGS. 4 and 5B. As in the example of FIG. 5B, thepre-ignition window may be split into three segments: a first segmentSeg_1, a second segment Seg_2, and a third segment Seg_3. The firstsegment may be termed an earlier segment relative to each of the secondsegment and the third segment. Further, the third segment may be termeda later segment relative to each of the first segment and the secondsegment.

Map 1000 depicts fueling of the single cylinder at plot 1002, an HSPIflag at plot 1004, sensor output from a knock sensor in the firstsegment of the pre-ignition window at plot 1006, sensor output from theknock sensor in the second segment of the pre-ignition window at plot1008, sensor output from the knock sensor in the third segment of thepre-ignition window at plot 1010, and engine speed at plot 1012. Plots1006, 1008, and 1010 present changes in the knock sensor output in thedifferent segments as the number of engine cycles increases with timealong the x-axis. Line 1009 represents a threshold speed for determiningHSPI. All plots are shown over time, along the x-axis. Further, timeincreases from the left of the x-axis towards the right and may alsoindicate an increase in the number of engine cycles. Note that elementsaligning at a common time on the graph, such as at time t1, for example,are occurring concurrently, including for example where one parameter isincreasing while another parameter is decreasing.

Between t0 and t1, the engine may be operating with a lower engine speedand abnormal combustion events may not be present, as indicated by thelow peak values of sensor output in each segment. Further, the cylindermay be fueled with a lower amount of fuel based on existing engineconditions. At t1, a sudden rise in engine speed may occur whereuponengine speed may increase to higher than the threshold speed (line1009). In response to the increase in engine speed and other conditions,fueling of the cylinder may increase. Further, knock sensor output inthe various segments of the pre-ignition window may change with the risein engine speed.

Immediately after t1, sensor output in the third, later segments of thepre-ignition window may include multiple peaks with higher peak values.At the same time, sensor output in the second, middle segments of thepre-ignition window may include medium peaks with moderate peak valueswhile the first, earlier segments of the pre-ignition window may includefewer peaks, wherein the peaks have considerably lower peak values. Asthe number of engine cycles increases with time, a change in peak valuesacross the segments may be observed if HSPI is present. Between t1 andt2, for example, peak values in the second, middle segment of thepre-ignition window gradually increase. Further, as the engine continuesto operate at higher engine speed between t2 and t3, peak values in thefirst, earlier segments steadily rise while a corresponding decrease inpeak values is observed in third, later segments of the pre-ignitionwindow (between t1 and t3).

As depicted by the dashed line 1017, peak values (e.g., peak heights) inthe third, later segments of the pre-ignition window gradually diminishas the number of engine cycles increases between t1 and t3 while peakvalues in the first, earlier segments of the pre-ignition windows risesteadily as shown by dashed line 1013 between t1 and t3. Meanwhile, peakvalues in the second middle segments rise and then fall, as shown bydashed line 1015. Thus, peak values in the later segments of thepre-ignition windows may decrease as combustion events occur earlier inthe engine cycles. Further, as combustion events transition towards anearlier timing of engine cycles, peak values in the earlier segmentssteadily increases. Responsive to the reduction in peak values in latersegments and a concurrent increase in peak values in earlier segments,HSPI may be indicated. Specifically, the HSPI flag may be activated att3 whereupon one or more mitigating actions may be initiated. Forexample, as depicted at t3, fueling of the cylinder may be terminated inresponse to the indication of HSPI. In addition, engine loads may belimited (not shown). Further, engine speed may also be limited byreducing intake air flow and/or by reducing fueling. Dashed section 1021depicts a reduction in engine speed to that of the threshold speed(represented by line 1009) between t3 and t4 in response to engine speedlimiting. HSPI may subside in response to the mitigating actions asindicated by the lower peak values in the sensor outputs between t3 andt4. Once HSPI is alleviated, fueling of the cylinder may be restored att4. Further, the limit on engine speed and engine load may be removed.Accordingly, engine speed increases after t4.

One example engine system may comprise an engine cylinder, a knocksensor coupled to the engine cylinder, a direct fuel injector forinjecting fuel into the cylinder, an intake throttle, and a controllerconfigured with computer-readable instructions stored on non-transitorymemory for measuring an output of the knock sensor in a first, laterknock window over a first number of engine cycles, measuring the outputof the knock sensor in a second, earlier pre-ignition window over asecond number of engine cycles, integrating the output of the knocksensor in each of the first, later knock windows and the second, earlierpre-ignition windows, indicating pre-ignition based on the integratedoutput in the first, later knock window relative to the integratedoutput in the second, earlier pre-ignition window, and adjusting anopening of the intake throttle based on the indication. In the precedingexample, the first number of engine cycles may additionally oroptionally precede, or may be concurrent to, the second number of enginecycles. In any or all of the preceding examples, the indicating based onthe integrated output may additionally or optionally include indicatinghigh speed pre-ignition responsive to one of an increase in theintegrated output in the first, later knock window followed by anincrease in the integrated knock sensor output in the second, earlierpre-ignition window, and a decrease in a peak value of the output of theknock sensor in the first, later knock window with an increase in thepeak value of the output of the knock sensor in the second, earlierpre-ignition window. In any or all of the preceding examples, the systemmay additionally or optionally further comprise a spark plug, whereinthe indicating may be additionally or optionally further based on achange in spark timing of the cylinder, the indicating includingindicating pre-ignition responsive to an increase in the integratedoutput in the pre-ignition window following the integrated output in theknock window exceeding a threshold and spark timing in the cylinderbeing retarded by a threshold amount.

Another example method for an engine may comprise indicatingpre-ignition based on each of an integrated knock sensor output in aknock window and an integrated knock sensor output in a pre-ignitionwindow. In the preceding example, the method may additionally oroptionally further comprise, in response to the indication, disablingfuel injection to an affected cylinder for one or more combustionevents, and then resuming fuel injection in the affected cylinder. Inany or all of the preceding examples, the method may additionally oroptionally include reducing an intake air flow to reduce an engine loadfor one or more combustion events in response to the indication, andthen resuming the engine load. In any or all of the preceding examples,the knock sensor output in the knock window may additionally oroptionally be compared to a lower threshold, while the knock sensoroutput in the pre-ignition window may be compared to a higher threshold.In any or all of the preceding examples, the integrated knock sensoroutput may additionally or optionally include an integrated knock sensoroutput value, and wherein the indicating additionally or optionallyincludes indicating pre-ignition based on a rise in the integrated knocksensor output value in the knock window followed by a rise in theintegrated knock sensor output value in the pre-ignition window. Inaddition, in any or all of the preceding examples, the method mayadditionally or optionally include indicating pre-ignition based on peakvalues of knock sensor outputs in each of the knock window and thepre-ignition window, and wherein the indicating may include indicatingpre-ignition based on a decrease in the peak values in the knock windowsand an increase in the peak values in the pre-ignition windows. Theindicating, herein, may be further based on a rate of change in theknock sensor output in the knock window relative to a rate of change ofin the knock sensor output in the pre-ignition window. As such, knocksensor output may be integrated over a common number of engine cycles ineach of the knock and pre-ignition window. Alternatively, the knocksensor output may be integrated over a different number of engine cyclesin the knock window relative to the pre-ignition window. The knockwindow may be a crank angle window that is non-overlapping with thepre-ignition window (as shown in map 410 of FIG. 4). In another example,the knock window may be a crank angle window that is at least partiallyoverlapping with the pre-ignition window (as depicted in map 430 and map450 of FIG. 4). As shown in FIG. 5B and routine 700, the method mayinclude dividing at least the pre-ignition window into a plurality ofsegments, the plurality of segments based on a degree of overlap betweenthe knock and pre-ignition windows. Herein, the indicating may be basedon a comparison of peak values of knock sensor output in each of theplurality of segments of the pre-ignition window over a plurality ofengine cycles. As such, indicating pre-ignition may include indicatinghigh speed pre-ignition.

In yet another example, a method for an engine may comprise indicatinglow speed pre-ignition based on knock sensor output assessed in each ofa knock window and a pre-ignition window, and indicating high speedpre-ignition based on an integrated knock sensor output, integrated overa number of engine cycles, in each of the knock window and thepre-ignition window. In the preceding example, the method mayadditionally or optionally further comprise, in response to theindication of low speed pre-ignition, enriching an affected cylinder andreducing engine intake air flow by a first amount, and in response tothe indication of high speed pre-ignition, deactivating fuel to theaffected cylinder and reducing engine intake air flow by a secondamount, the second amount higher than the first amount. In any or all ofthe preceding examples, the method may additionally or optionallyfurther include, in response to the indication of low speedpre-ignition, the affected cylinder may be enriched for a first, smallernumber of combustion events, and wherein in response to the indicationof high speed pre-ignition, fuel may be deactivated in the affectedcylinder for a second, larger number of combustion events.

In this way, high speed pre-ignition may be distinguished and mitigated.A technical effect of identifying and remedying high speed pre-ignitionpromptly is reducing issues such as runaway pre-ignition and associatedengine degradation. High speed pre-ignition may be detected via one ormore of analyzing changes in integrated knock sensor outputs in knockand pre-ignition windows as well as by evaluating changes in peak valuesof knock sensor outputs in knock and pre-ignition windows over aplurality of engine cycles. As such, high speed pre-ignition may be moreaccurately identified without corruption of knock sensor output frommechanical noise during higher engine speeds. Overall, engine durabilityand performance may be enhanced.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A method for an engine, comprising: indicating pre-ignition based oneach of an integrated knock sensor output in a knock window and anintegrated knock sensor output in a pre-ignition window.
 2. The methodof claim 1, further comprising, in response to the indicating, disablingfuel injection to an affected cylinder for one or more combustionevents, and then resuming fuel injection in the affected cylinder. 3.The method of claim 1, further comprising, in response to theindicating, reducing an intake air flow to reduce an engine load for oneor more combustion events, and then resuming the engine load.
 4. Themethod of claim 1, wherein knock sensor output in the knock window iscompared to a lower threshold, while knock sensor output in thepre-ignition window is compared to a higher threshold.
 5. The method ofclaim 1, wherein the integrated knock sensor output includes anintegrated knock sensor output value, and wherein the indicatingincludes indicating pre-ignition based on a rise in the integrated knocksensor output value in the knock window followed by a rise in theintegrated knock sensor output value in the pre-ignition window.
 6. Themethod of claim 1, further comprising indicating pre-ignition based onpeak values of knock sensor outputs in each of the knock window and thepre-ignition window, and wherein the indicating includes indicatingpre-ignition based on a decrease in the peak values in the knock windowsand an increase in the peak values in the pre-ignition windows.
 7. Themethod of claim 6, wherein the indicating is further based on a rate ofchange in knock sensor output in the knock window relative to a rate ofchange of in knock sensor output in the pre-ignition window.
 8. Themethod of claim 1, wherein knock sensor output is integrated over acommon number of engine cycles in each of the knock window and thepre-ignition window.
 9. The method of claim 1, wherein knock sensoroutput is integrated over a different number of engine cycles in theknock window relative to the pre-ignition window.
 10. The method ofclaim 1, wherein the knock window is a crank angle window that isnon-overlapping with the pre-ignition window.
 11. The method of claim 1,wherein the knock window is a crank angle window that is at leastpartially overlapping with the pre-ignition window.
 12. The method ofclaim 10, wherein at least the pre-ignition window is divided into aplurality of segments, the plurality of segments based on one or more ofa degree of overlap between the knock window and the pre-ignitionwindow, engine speed, engine load, and spark timing, and wherein theindicating is based on a comparison of peak values of knock sensoroutput in each of the plurality of segments of the pre-ignition window.13. The method of claim 1, wherein indicating pre-ignition includesindicating high speed pre-ignition.
 14. A method for an engine,comprising: indicating low speed pre-ignition based on knock sensoroutput assessed in each of a knock window and a pre-ignition window; andindicating high speed pre-ignition based on an integrated knock sensoroutput, integrated over a number of engine cycles, in each of the knockwindow and the pre-ignition window.
 15. The method of claim 14, furthercomprising, in response to the indication of low speed pre-ignition,enriching an affected cylinder and reducing engine intake air flow by afirst amount, and in response to the indication of high speedpre-ignition, deactivating fuel to the affected cylinder and reducingengine intake air flow by a second amount, the second amount higher thanthe first amount, the reducing of engine intake air flow limiting enginespeed and engine load.
 16. The method of claim 15, wherein in responseto the indication of low speed pre-ignition, the affected cylinder isenriched for a first, smaller number of combustion events, and whereinin response to the indication of high speed pre-ignition, fuel isdeactivated in the affected cylinder for a second, larger number ofcombustion events.
 17. An engine system, comprising: an engine cylinder;a knock sensor coupled to the engine cylinder; a direct fuel injectorfor injecting fuel into the engine cylinder; an intake throttle; and acontroller configured with computer-readable instructions stored onnon-transitory memory for: measuring an output of the knock sensor in afirst, later knock window over a first number of engine cycles;measuring the output of the knock sensor in a second, earlierpre-ignition window over a second number of engine cycles; integratingthe output of the knock sensor in each of the first, later knock windowand the second, earlier pre-ignition window; indicating pre-ignitionbased on the integrated output in the first later knock window relativeto the integrated output in the second earlier pre-ignition window; andadjusting an opening of the intake throttle based on the indicating. 18.The engine system of claim 17, wherein the first number of engine cyclesprecede, or are concurrent to, the second number of engine cycles. 19.The engine system of claim 18, wherein the indicating based on theintegrated output includes indicating high speed pre-ignition responsiveto one of an increase in the integrated output in the second, laterknock window followed by an increase in the integrated knock sensoroutput in the first, earlier pre-ignition window, and a decrease in apeak value of the output of the knock sensor in the second, later knockwindow with an increase in the peak value of the output of the knocksensor in the first, earlier pre-ignition window.
 20. The engine systemof claim 17, further comprising a spark plug, wherein the indicating isfurther based on a change in spark timing of the engine cylinder, theindicating including indicating pre-ignition responsive to an increasein the integrated output in the second, earlier pre-ignition windowfollowing the integrated output in the first, later knock windowexceeding a threshold and spark timing in the engine cylinder beingretarded by a threshold amount.